What do you want to accomplish in making the determination? Children that young don't make it up on their own, although they do act out what was done to them or what they have seen, probably in an effort to try to make sense of it and understand it. Of course both children would have been affected by premature sexual exposure, and both should have had guidance or treatment to help deal with it. If treatment wasn't given then, both probably still have confusion and hurt, which can get harder to deal with over time when it wasn't properly addressed, and both probably need to talk to someone about it. Blaming one or the other child is not likely to be healing for anyone. It happened, and it affected both of you, and you can identify the results of it and address what needs to be addressed.

The 14-year-old was old enough to know better, although chances are that he was also victimized by someone. Abuse comes in cycles, and there is a reason why people do the things that they do. If the cycle is continuing, intervention needs to happen to stop it and keep other children from being hurt.

At six or seven years old, you were a child and someone else was responsible for what you did, not you.