The first film has Scott's ex-wife finally realising that he is Santa Claus and burning their son's custody papers.
For a lot of the movie, Scott just won't believe what's happening to him. It's very heartwarming when he finally accepts it and tells Charlie that.
"I love you, Santa Claus."
Bernard's moments with Charlie. He treats him like a little brother by giving him a special snow globe and giving him a room to stay in. Since he is Santa's head elf, it only makes sense that he's a Friend to All Children.
Though it was a funny Jerk Ass moment, it became a heartwarming moment when he revisited the little girl he was rude to, now accepting that he is Santa.
Scott: This milk it's a little sour.
Girl: It's Soy milk, you said you were lactose intolerant.
Scott: I did say that, didn't I? Merry Christmas.
Scott and Comet were at loggerheads in the first act, but by the end, when Scott has accepted becoming Santa, he tells Comet that he really appreciates Comet's gift of a rope to prevent his death by rooftop fall.
In the second film, Scott uses Santa's magic to give a bunch of adults a chance to let their inner child out by giving them the Christmas presents they loved most when they were little. Heck, just Scott pulling out all the stops on his first date with Carol in general. In addition to the secret Santa at the party (which involved him getting her the toy she told him about an hour ago), he gave her a sleigh ride, fresh falling snow, and mistletoe, even when he didn't need to. It didn't work as he wanted to but it's the thought that counts.
The relationship Scott and Lucy have. The fact that she calls him "Uncle Scott" even though they're not related and she's not his step-kid or anything. It's adorable.
Charlie going out of his way to tell Carol not to reject Scott just because she doesn't believe he's Santa Claus. Charlie hated her (since she was his no-nonsense principal) and felt betrayed that Scott was dating her... but still wanted nothing more than for his dad to be happy.
In the third film, after Scott has fixed everything and become Santa again, the first thing he does is immediately make up with Carol and her parents after the argument they had earlier.