I'm so sorry your son got hurt! Sounds like it's time for lots of pain killers and video games
Like PP, I just have to add my two cents here, for what it's worth ...
I think you need to be very careful about allowing your son to be in compromising situations like letting him wrestle with any daycare child (let alone a girl) on his bed! If any accusations were to come out of it, it could ruin his reputation and even his life. Even being accused of any form of abuse could damage his chances of getting a job, etc.
Even if the parents of this child would never accuse him of anything, what if another daycare parent, neighbour or friend of your son's heard about it and reported it?
I have two sons too, and even though they're not teenagers yet, I'm very careful about the situations I allow them to be in. Because it doesn't always matters what IS happening -- it matters what people THINK might be happening.