In episode 7, when Pop wets herself and is crying, Doremi is watching and selflessly uses her last magic ball to make a magic washing machine for her sister. Awwww.
Episode 2 of Sharp, Doremi and her mom share a bath while discussing the hardships and joys of being mothers, which dives into a mild Tear Jerker as Doremi's mom reveals that a Career-Ending Injury ruined her dream of taking up the piano, resulting in a suicidal depression. Being pregnant with Doremi however, inspired her not to give up.
Doremi encouraging her sister to take piano in the Sharp movie after telling her why their mom didn't teach her. Cue episode 40.
"Hana-chan, I love you. Daisuki yo..." "...Momo..."
Episode 45 of Motto!, Kayako, who's spent most of the season trying to deal with her problems with going to school, manages to talk with the people who caused the problem and make up. The episode culminates with her being supported by both 5th Grade classes and going into the classroom. Also doubles as a Tear Jerker
During episode 12 of Naisho, Doremi has a snowball fight with Non-chan's mother. The reason? To carry out Non-chan's wish after she died, as Non-chan's mother promised to have a snowball fight with her when she recovered. Doremi carrying it out allowed Non-chan to fulfill that promise through Doremi. Has to be seen to be emotional.
A little kid from the hospital who was a friend of Non-chan is seen recovering at the end of the episode. Doremi hugs him.
Baba showing how much she cares for Laura during Dokkan episode 34 by retrieving her scarf after it was blown away.
The whole series is built around these, as most of the episodes are about the girls helping their classmates/family with their problems. In the fourth season it even becomes a main plot point for them to reawaken the heartwarming memories of Majo Tourbillion.
Akira healing Reiko's heart in her backstory. To elaborate, Reiko was a Meal Ticket for a JerkassGold Digger who basically went after her For the Evulz and broke her just to rub salt in the wound. Akira coming in and being accepted by Reiko's mother along with him being an overall genuinely AdorkableNice Guy helped heal that wound.
When Doremi slips and falls on a flight of stairs said to curse anyone who does that with bad luck, Kotake intentionally slips and falls on the same flight so that Doremi wouldn't be cursed alone.
In Episode 13 of Naisho (which technically counts as the last released episode of Ojamajo Doremi), Doremi becomes fast friends with another girl named Fami on Hinamatsuri (Girl's/Doll's Day). She introduces Fami to the rest of her family, and they celebrate the holiday together. At the end it's revealed that Fami herself is a witch apprentice, as well as Doremi's granddaughter from the future. With the Empress doll Doremi had since she was a toddler, Fami traveled back in time to meet her grandmother's younger self, and also confirm that Doremi herself was a magic-user. In the penultimate episode of Dokkaan, it was Doremi's wish to be able to pass on tales of magic and witches being real to her children and grandchildren, and it's incredibly sweet seeing her in Fami's memory passing on the Hinamatsuri blessing of her family to her granddaughter.