Freddie showing up at the train station and proposing to Ada. It's going to gobadly, but it's sweet.
In 1.03, the look on Freddie's face when he sees Ada in her wedding dress. He tells her she looks like an angel.
Finn falling asleep on Polly's lap.
Polly attempting to get Freddie and Ada out of England multiple times, trying her damnedest to avoid the bloodshed that will occur if Tommy has to deal with the situation.
Tommy buying the Garrison and giving it to Arthur to run. It'll help with Arthur's PTSD and depression over being basically superfluous to the Peaky Blinders (now that Tommy's in charge), and Arthur's apparently always wanted to own a bar.
Tommy's attack of conscience over whoring Grace out to Billy Kimber. The precise way he gets her out of sleeping with Kimber may be embarrassing for her (he lies and tells Kimber she's got the clap and that's why Kimber can't have sex with her), but the fact remains that he realized Grace shouldn't just be a pawn to him.
How panicked Tommy gets when he realizes where the Lees have wired the grenade, and his frantic attempt to get Finn out of the car. Even though the wire gets tripped and the grenade goes off, Tommy scoops Finn up protectively.
John's wedding, after the arrangement part and before Ada picks a fight with Tommy. Peace is mostly achieved between the Lees and the Shelbys, and everyone's happy and drinking and dancing.
Ada giving birth to a healthy baby boy, and Freddie holding his son for the first time.
Tommy "not hearing the shovels" (a part of his PTSD) while lying in bed with Grace after sex. Sure, they seem kind of doomed, but it's still a sweet moment.
Polly calming baby Karl for Ada, sharing some mothering tips. Takes a swerve into Tearjerker, though, when Polly tells Ada just what happened to her own kids.
Ada showing off baby Karl (for Marx, of course) to her family and the rest of the Peaky Blinders, and Arthur racing over to hold the baby. He even puts his cap on the baby's head.
Freddie deciding to join Tommy and the Peaky Blinders in the battle against Kimber, despite Tommy getting him thrown in jail the night his son was born and trying to kill him.
Grace telling Tommy she loves him and asking him to run away to New York with her.
The three boys and Polly getting drunk in the Garrison together after the battle with Kimber's men. Polly says it was a good day and that there will be others, and Tommy breaks out the champagne he'd had Grace save, toasting "to the others".
The Shelby Company is making 150 pounds a day, expanding to London, employing over 200 people, and money is flowing enough for the Shelbys to own four Bugattis and numerous drivers for them. But the money isn't safe from rivals, so what does Tommy do? He buys his sister and nephew a house in London, and Polly a house in Birmingham.
Ada walking into her own house for the first time, and whispering "silence at last".
Polly being so overwhelmed by the house, and Tommy sitting her down and telling her the real reason he's bought it.
Tommy: I know you haven't been happy for a while, and I know why… I've spoken to our contacts in the police, and they have contacts in the council. Contacts with the people who keep the parish records. Records of adoptions, and of confidential forced removals. Now, with your permission, I'd like to grease a few palms and take a look at the records they never showed you. Pol, I'm going to find your son and daughter, and I'm going to bring them home. That's what this house is for—so that you can bring your family home where they belong. We're moving up, Pol.
The Shelbys celebrating Michael's 18th birthday in the Garrison, and how proud Polly looks of him. Also, Tommy being a substitute father-figure and giving Michael a watch.
Ada worrying over Tommy, reassuring him in episode six, when the shit is about to hit the fan, that she and the rest of the family love him.
Jeremiah presiding over Tommy's and Grace's wedding.
The sheer enthusiasm and happiness of all the Shelbys during the wedding, despite the bad blood between them and the cavalry officers, as well as between them and Grace.
Tommy reassuring Arthur that he loves him, even when he's embarrassing Tommy:
Tommy: Fuck the speech, okay Arthur? You're my best man every fucking day.
Arthur's speech, stumbling and awkward as it is, makes it clear how much Tommy means to him.
Tommy spending a day with Grace and their son Charles, teaching the little boy how to feed horses and goldfish.
3.06 is really, really bleak, but a bright spot is Tommy finally acknowledging Lizzie's importance in his life.
Polly admitting to Reuben that she wants a "normal life, a dull life" with him, and that she'd give up the business for him. His smile just about lights up the room.
Curly's belief in 4.02 that there's a bright spot in the darkness:
Curly: We've got grenades and guns and Polly's back, so everything's going to be okay.
Tommy allowing Finn a seat at the bosses' table for the first time, chiding Arthur for his "shut up Finn" Catch-Phrase.
Polly reminiscing about the days of her youth at the campfire with Aberama Gold. And then seducing him - without any ulterior motive, just because she finds him attractive and feels free to do whatever she pleases. It's very human.
Aside from some signature teasing and sarcasm, the Shelby ladies (Polly, Ada, and Linda) congratulating Lizzie on her pregnancy and joining the family is a sweet gesture.
Tommy's maid, Frances, being so concerned about Tommy during his "vacation," during which time he suffers flashbacks and reveals how much of a Shell-Shocked Veteran he is, that she calls Polly. And Polly comes to his aid. Doubly heartwarming if you consider where Tommy and Polly stood at the start of the season.