I take my son to superhero films only to look at cosplay girls and take photos with them
Thats a bit creepy. What about women in cosplay appeals to you?
I'm a fan of S & M stuff.
Your child will never forget the fun times you brought him to, but having an underlying cause for it is somewhat devious. Especially if it is to stare at and take photos with Cosplay girls. It needs to stop right now, your son will catch onto it and think it's okay to do things just for this reason alone.
It's harmless. He probably won't remember about that on his own.
It's not harmless if the women at these events feel creeped out at your presence. You're also teaching your son that its okay to leer at women. Your behavior often gets passed onto your children so you should keep that in mind.