In the movie, Scott Calvin's (Santa Claus) son, Charlie, witnesses Santa kissing his mom (Scott's ex-wife) and becomes convinced that Santa is trying to break up his family. Charlie tells Scott that he is a "home wrecker" and that Santa is ruining Christmas.
This leads to a conflict between Scott and Charlie, with Scott trying to convince Charlie that he's not trying to steal his mom and that he's just a good friend to her.