OK. I call this a bluff - either the police are quite literally SO BORED, there must no crimes in the entire state right now or they're damn well mentally retarded.
There are just so many things wrong with this...
One, to say the least it's clearly a case of self-defense, and he was provoked so if he was an adult say then really that's what it should be - hell! I've seen some women kick men in the crotch just for asking for politely asking for their number at a bar, and damn nobody even batters an eyelid - forget charge her with sexual harassment!
Secondly - probably the most important one. THE KID IS DAMN 7!! Seven years old! What is this!? I wouldn't care if he groped a women boob while slapping her on the ass - the kid is 7 for the love of god! He's no way near responsible for his actions yet!
Isn't there like a legal standard that you either have to be a psychopath or 10 to even COMMIT a crime? Even 10 would be a stretch, but the kid is 7! He's not even got into a proper school yet! (I think at least I don't follow the American Education system) I mean really what is this?!
Finally, these things happen all the time, why on earth pick on this one case, why does it even need investigating?! I don't care if that 'Victim' who got punched in the crotch has lost his ability to have kids in the future - if you're going to be a dick you probably deserve it! There are knife crimes, gang wars all over the damn world, is this REALLY a first priority here? Seriously! It sounds like someone whacked the coppers over the head with a potato!