well we just found out about the history of this after he had already done this. My usband was doing dishes they were playing in the playroom
I'm surprised they were left unsupervised if he had a history of doing this.
Curiosity is normal, but the gap in ages is worrying. I would talk to your pediatrician about the boy and ask him/her what you should do. Obviously, you won't be leaving them alone together anymore, but maybe you can refer your husband's cousin to someone if your pediatrician thinks it's in order.