My half-sister's daughter lived with us from the time she was six months old, until she was seven years old. I was the youngest and my sister was the oldest, so I was about nine when Amy (not her real name) was born.
One evening when Amy was about six she was playing on the floor with her dolls. My dad was sitting in his big easy chair reading, as were my older brother and I. We were all engrossed in our books when I happened to look up and notice that Amy had disappeared. Well, sort of anyway, as I saw one of her feet sticking out from behind my dad's chair.
Being curious, I slid down from the sofa and crawled over to look behind the chair. There sat Amy, leaning against the wall, her knees up and spread wide apart, with her skirt around her waist. She was holding the crotch of her cotton panties to the side with her left hand and fully exposing herself, while she fingered her swollen clitoris with her right hand. She saw me almost immediately and jerked her skirt down. I told her softly that she should only do it in her room. She jumped up and ran off.
I never mentioned it to her or anyone else in the family. Obviously she took my advice and never did it in the open again. It was just a one-time event.