Threatening/killing their children/adopted children is one of the few things that can tempt a DCU hero, either male or female, that normally follows Thou Shalt Not Kill to, well, kill. When Black Canary's adopted daughter Sin apparently died during a kidnapping attempt by the League of Assassins, Dinah went berserk and nearly killed Merlyn, the mastermind of the scheme.
The female Dr. Light proved her Mama Bear status in print, in an alternate timeline in a recent issue of Booster Gold, by killing the evil Max Lord for killing her kids. And thus, Fanon becomes semi-Canon: Don't mess with Kimiyo Hoshi's children!! In the main timeline, when the superpowered zombie Dr Arthur Light threatened her children, Dr Light was able to create a bright and powerful enough light to completely atomize him.
Leetah in ElfQuest is a healer who has lived most of her life in the peaceful desert oasis of Sorrow's End, until she and her family get caught up in the titular quest. When their party is attacked by trolls, she has no choice but to kill one of them who's threatening her daughter, even though it causes her a lot of soul-searching afterward.
Considerably less soul-searching occurs when Rayek makes the mistake of abducting her into the future, then dismisses her love of Cutter. "He. Was. My. -SOUL-!!!" Rayek very quickly finds out that Winnowill has nothing on an enraged Leetah.
Snow White in Fables. When Geppetto asks why she stood against him when he did nothing personally to her, she responds "You threatened my cubs. Do you think I would hesitate to throw a thousand worlds into chaos to protect them?" Following that, Bigby even refers to her as "Mama Bear".
And in "March of the Wooden Soldiers," when Geppetto's wooden army is attacking Fabletown, and Boo Bear is killed, a few panels farther on you see his mother, in the thick of the fighting, screaming "And This Is for... my Boo Bear, you monsters!"
Later on, in another arc, after Smug Snake Prince Brandish claims Snow's hand, and defeats Bigby Wolf, Snow, even fighting injured and with her non-dominant hand, outfights him and defeats him in a sword-to-sword duel. Why? Well, he'd made it clear he was going to kill her children!!!
One issue of Fantastic Four had Reed and Susan's daughter Valeria caught in the middle of a rampage created by Thundra, the Absorbing Man, and a mind-controlled Ben Grimm and She-Hulk. She's about to be squished when Sue shows up, already in a bad mood. Cue the resulting stomping of four of the most powerful superhumans on Earth. Made even better when Reed and Johnny show up...and Reed restrains Johnny from trying to help Sue, because he knows that she's not going to need any.
Sue could practically be the goddess of this trope. In the Fantastic Four Vs. the X-Men miniseries, the team is nearly torn apart when an old diary of Reed's seems to imply that he caused the accident that transformed them into the FF on purpose. It's Sue that deduces the diary is a trap laid by Dr. Doom years before. She warns Doom that a lioness is "never as dangerous as when protecting cub, and den, and mate." She then asks Doom if he's ever considered just what would happen if she decided to project an invisible force-field inside his body...and then expand it.
Add to this the fact that Reed is a Papa Wolf himself, and it's a given that threatening Franklin and Valeria is death wish.
Julia Diggers goes Mama Bear on the assassin Zero when he attacked her first student Gar, who's as close as a son to her, resulting in one of the epic battles of the entire series. One almost feels bad for Zero because he gets put in line of Digger's parent rage not once but several times, and he doesn't even have anything against them, it's just nessesary for his bosses' and thus his ultimate goals.
Werewolf mom Jetta when her son Pojo is abducted. Then again, not only is she a rather traumatized individual of a species bred to be violent killers, she is also the only female capable of her species capable of having children, and Pojo is her newborn, first child. All things considered, her reaction was one of thoughtful consideration, really.
A very grim example: in Hack Slash Cassie Hack's mother was so outraged when her daughter was bullied by popular girls at high school that she murdered them all as The Lunch Lady Killer. And she was so outraged that, after being caught and committing suicide she came back from the dead to carry on, forcing her daughter to rekill her.
Huntress (Helena Bertinelli) demonstrates this when her students are threatened. With added holding villains off rooftops for fun!
Kate Spencer AKA Manhunter will kill anyone who hurts her son.
Michael Tree, the heroine of Ms. Tree, will go medieval on the ass of anyone who threatens her stepson Mike or, later, her daughter Melody.
And her Evil Counterpart, mob boss Dominique Mureta, is equally violent in the defense of her daughter.
When the Mane 6 finally get to rescuing the CMC in issue #4, Rainbow Dash is shown to be protecting Scootaloo as frequently as the above sister pairings. Consider that continuity-wise, this arc pre-dates "Sleepless in Ponyville" where the relationship was made more explicit.
A literal Mama Bear is shown in a two comic arc by Kevin J. Anderson featuring a Predator taking on an angry mother grizzly. After the Predator blasts one of her cubs, he's ambushed by the furious mother and, despite his technological advances, eventually succumbs to her ferocity.
The Punisher story arc Streets of Laredo features a mama bear in the form of Rachel, the leader of a big-time gunrunning outfit in Texas. The only thing she cares about more than her operation is her son, Clark. Clark is openly gay, and when one of Rachel's men voices his contempt she challenges him to a fight and coldly beats him to death.
Mary Jane Watson-Parker had a similar one in Spider-Girl: She's attacked by the new Green Goblin (Harry's son, Normie), who intends to kidnap and use her as bait for her daughter, the titular heroine. MJ just refuses to play along, and beats him with a lamp while lecturing him about how childish he was being (Paraphrased from memory: "I used to change your diaper, what makes you think I'm going to be scared of you!?"); Normie is completely thrown off, and tries to apologize before Spider-Girl then swings in to the rescue. Which one she's rescuing is a bit unclear by this point.
Despite being villains themselves, the Pride do everything in their power to keep their children safe in Runaways. In one story arc, the group gets stranded in the 1800s and Chase meets the past selves of the Yorkes when they were time traveling to that era. He angrily informs them that their daughter is dead in their future, his present (in their time, Gertrude still has about two years left). Stacy and her husband make immediate plans to save their daughter from this fate and bring a nuclear bomb to the city to get revenge for Gertrude dying in any of the possible futures.
The Sandman: When Hippolyta's son Daniel is taken to be the next incarnation of Dream, she loses her mind and recruits the Furies to take revenge on the original Dream, leading to his death. To be fair to Hippolyta, she only goes this far when she thinks Dream burned her son to death. When she realizes that Daniel is still alive (only his mortality was burned away), she tries to get the Furies to stop their attack and help her get him back saying that they don't have to kill Dream. The Furies tell her that they don't help, they avenge and continue on their campaign unabated.
Even Aunt May Parker has demonstrated this line of abilities when somebody messes with her dear nephew and adopted son, Peter Parker, AKA Spider-Man. When the Chameleon, a ruthless assassin and skilled infiltrator, tries to take Peter's place, she not only manages to subdue him in an undeniably classy fashion, she also scares the bejeezus outta him in the process.
And in another storyline, when the Vulture broke into their house and threatened them with a gun, after Peter managed to disarm him of it (trying hard not to show his full strength and give his identity away) she picked the weapon up and pointed it at the criminal, and ordered him to leave.
Her Ultimate Universe version (admittedly, rather feistier than the original), responded to J. Jonah Jameson merely firing Peter Parker by ...asking to speak to him on the phone. Afterwards, Jameson revoked the firing and balefully told Peter not to put him on the phone with his Aunt ever again...
More recently, when Ultimate Eddie Brock/Ultimate Venom showed up at the Parkers' home, attempted to talk his way inside (reminiscent of a scene that occurred in the mid-90s animated series where the beefier inspired-by-616 Brock does the same to a quite-different Aunt May.) The conversation does not go well for Ultimate Brock. She pulls a hand cannon on him and threatens to blow him away, knowing what he is.
Sure, her son's one of the most powerful non-god beings on the planet, but do NOT mess with Superman when Ma Kent is around. She probably won't be of much use, but damn if she won't try. Pa Kent'll provides backup as a Papa Wolf - and he's got military experience.
Nomi Sunrider in Tales of the Jedi. This is how she gets started on the path to Jedi-dom; she picks up her murdered husband's lightsaber to defend their daughter from a bunch of space thugs.
In Teen Titans, Adeline Wilson takes this to a pretty scary level. After her husband, Slade lands their son Jericho in a hostage situation (that ends with their child being rendered permanently mute due to his throat being slit), Adeline shoots Slade in the head. Another, even more extreme example (Though it may not count since she had just gained super powers that made her so psycho) occurred when she tried to destroy every super powered person in the world to avenge Jericho's death.
In the "Rise of the Olympian" story arc, Wonder Woman destroys the Secret Society's headquarters with her bare hands after their creation Genocide captures and tortures Etta Candy with her own lasso.
Subverted in the X-Men comic books. Jean Grey is — in certain continuities — the mother of Rachel Summers. Very rarely does Jean ever lift a finger to protect Rachel. This is probably because Rachel is a psi of talent close to or exceeding her mother's own. Baby can take care of herself and Mama knows it too well. Plus, Mama's dead a lot.
But then played straight when Jubilee starts having nightmares about Sabertooth, who is being held on the grounds at the time. Jean confronts the captive Sabertooth, walks in to his cell, and proceeds to break every bone in his body without lifting a finger. Don't threaten Jean's family. Just don't.
Jean: You are a firecracker, I am an atom bomb.
Played straight with Ororo Munroe aka Storm in the '90s X-Men animated series, when her god-child (the son of Storm's best friend in Africa, whom she has known from birth) who's also a mutant (more exactly, a Fragile Speedster a la Quicksilver) is kidnapped and possessed by her arch-nemesis, the Shadow King. Used a bit in X-Men: Evolution, too, where she was Evan/Spyke's Auntie Bear of sorts an the Team Mom of the group.
Though not ordinarily thought of as having a particularly motherly attitude, Emma Frost of all people. To say that she does not take kindly to people threatening or harming her students is an understatement. Given that her entire first class of pupils was murdered, that's not a shock, and it's been strongly insinuated several times that there are no lengths she won't go to in keeping her current "kids" safe.
And she shot her own sister in Generation X after said sister's actions resulted in the death of one of her students.
The reason she gave X-23 such a hard time when she first arrived at the Institute was because she thought X-23 was a danger to the other students. Since X-23 is a Tyke Bomb with a body count to her name and goes berserk when exposed to a certain chemical trigger that the Weapon Plus program still has (which is so indoctrinated into her brain that Emma can't undo the conditioning), Emma isn't exactly wrong. She definitely Kicked The Puppy when she tormented X-23 with visions of the mother figure X-23 killed under the influence of the trigger scent to show X-23 that she didn't belong at the Institute...but later she does come around though, as she eventually sees that X-23 is just another student who needs her protection. In fact, she finds Kimura (X-23's abusive former 'handler') and erases her only happy memories before sending Kimura to kill everyone at the Facility, starting with the poor SOB who kidnapped her pupil Mercury. Don't frak with Frost.
It's come to the point where almost any time Emma makes an appearance in a book focusing on X-23, it's so that the latter can serve as Emma's Morality Pet.
Her first class of pupils (but one) was murdered (the Hellions), and then Everett and Angelo from her second class (Generation X), then the entire third class (in Genosha)...and lately she lost a big chunk of her fourth class (45 students at Xavier's school where she was the headmistress), mostly because of the School Busof death.
This trope first comes into play when the Green Goblin attacks her while she's pregnant. She freaks out, thinking he's killed her unborn baby, grabs his gilder from beneath him while he's in the air and then wallops him with it. Spider-Man's reaction is "Whoa."
It comes into play again in Young Avengers when Kang threatens her. She attacks him and steals his weapon, telling him to never threaten a pregnant woman. Later, when the changes to the timeline temporarily erases her pregnancy, she attacks him again, demanding to know what he did with her baby.
During the events of Secret Invasion, she gives Dani to Jarvis for safekeeping while she helps her husband fight the bad guys. When she discovers that Jarvis was actually a skrull who has kidnapped her daughter, she goes on a rampage trying to find her.
In Mighty Avengers, when Superior Spider-Man confronts Jessica and Luke while they're with Dani, they arrange for a babysitter to pick her, then start whaling on him for putting her daughter in harm's way.