since After Bruce put Damian in a private school, he noticed that he always saw a child who stayed out of school longer... besides his appearance was a little strange

Bruce also began to notice that when the joker got out of prison, his son simply disappeared, he didn't commit any crime until the joker was caught again

Bruce then started to associate some things like that, so one random morning when Bruce took Damian to school

He said goodbye to his son but instead of leaving he stayed Looking at you from afar, until he decided to get closer to see if you were really the Joker's son

“Excuse me child, class is about to start, shouldn’t you go in?” Bruce asked keeping a social distance from you, he didn't want to seem threatening, after all you were still a child