Signs of ual abuse on a 2 year old?

I'm worried about my granddaughter. She's 2 and her real dad has just recently begun taking her for visitation but she's been doing odd things like laughing when you change her and wipe her with a baby wipe and just tonight she put her "private area" in her 11 month old brother's face and held his head there, she did have her diaper on but still I'm worried. Any ideas? I want to ask her questions but she's at the stage where when you ask her stuff she repeats you and doesn't really answer so it's kind of hard.