Sexual Abuse Support Group
Sexual abuse is a relative cultural term used to describe sexual relations and behavior between two or more parties which are considered criminally and/or morally offensive. Different types of sexual abuse involve: Non-consensual, forced physical sexual behavior such as rape, incest or sexual assault, or psychological forms of abuse, such as verbal sexual behavior or...
Lots and lots of kids do the same sorts of things, and yes, at a young age. There are cases where a child is abused and then acts out on siblings or friends, but there's usually an age or power difference and the abuse is non-concentual. You sound like a perfectly well adjusted young lady who played doctor a few times like millions of others.
The key issue is how it made you feel. If you feel dirty or used, or like you were a "bad girl" then you should probably discuss the incidents with a therapist. If it's just a memory and you're fine with it don't sweat it.