I walked in on a boy being molested in the bathroom
Do you know who they were?
Yes. My parents think it might be uncle Bill
That must be hard to deal knowing a close relative is doing that. If you're uncle really is doing that, your parents have to take action to stop him.
I think I will make it my life mission to hurt my uncle.
You should not try to hurt your uncle, but I do think that he needs to be reported. He should not get away with sexually abusing young children.