Safe hugs if ok. Yes it was SA. You were a child and didn't know any better, you thought it was a game. You said that yourself. The babysitter knew what he was doing, and did it anyway. It doesn't matter what you did or didn't know. HE knew. I am sorry that you had to go through that, your brother too.

One day, when you are ready, you will be able to talk about it in RL. For now, this is a great place to talk and get it off your chest. Maybe you could print this post out and show it to your T when you are ready. That way you don't have to speak it unless you want to. Sometimes it is easier to allow someone to read what happened than to verbally say it.