4 year old humping 3 year old?

We had a sexually abused six year old fd. She had been exposed to various activities as well as victimized by various children and adults. We knew the history we didn't know what it would look like for her to sexually act out. (we weren't told she did this and weren't ready for it). Dry humping stuffed animals, using various objects just to name a few. I had a hard time, my husband had a hard time...I felt really guilty for being so "grossed" out. I think that reaction is somewhat normal. It's hard to imagine little kids as sexual let alone to see it. Good luck my heart goes out to you and all of the kids