My daughter got fingered

My friends son and my daughter had a play date they were in lexi(my daughter)s room upstairs and I was downstairs with my friend they had been very quiets for 10 mins so I went up to check in them I peeped through the crack on the door and saw Elliot (4years old )with his finger in my daughters vagona and lexi was lying on the bed with her skirt up and her legs spread apart I just pretended I didn't see anything and shouted up to the that dinner was ready what do I do help