Blaaaah! Molested :(

I'm watching my nieces and one came to me crying at 3am because she had to tell me her moms baby sister who is a male, touches their private parts. I'm so sad and disgusted. My nieces are 7 and 8. Just need some kind words. My nieces are everything to me and I'm just sick that this happened. I don't know how to go about asking them questions about it, or do I not? I'm getting a hold of the police today.