You were six. You were curious and it sounds like you were niave'? Did it happen everyday/night? Much of sexual abuse is perpetrated by children to children. It sounds like it has bothered you, so you may have known it was wrong. Does your brother talk about it? Is he okay today? You should talk with a professional counselor about these events. It sounds like you may need to get this off your mind and resolve it. God Bless.