I try to always be honest and open with my four year old. I told her that boys and girls have different body parts and we made names for them, she knows where her sister came out when i went to the hospital to have my youngest daughter. She has told me when i went to work and left her with her uncle that she saw them having sex. I have never explained what that is , but I have now caught her with my three year old son two times closed in a closet with no clothes on and touching eachother. I lost it...i told her that that is her brother and it is not ok to touch eachother like that...I dont know what to do from here and what to do if it happens again.