Definitely get some sort of video camera set up, and get something recorded. Ask around the neighborhood, and see who else has had problems. It's unlikely you are the first, or this will be the end of it. They are going to get worse, until the police catch them. Worst the courts will give you is probation and a record. Too bad you posted this publicly, never admit to anything, let them prove it.
I'm 6'4", and a little over 200 lbs, so seldom get into anything physical, not to mention I like large breed dogs. Sometimes I run into people that talk a lot of trash, but its just words. Cats are cheap to replace, but are usually pretty good at taking care of themselves. My Siamese would have scratched them silly, she had no fear.
Anyway, if a kid gets physical with me, he's going to be dealt with like an adult, and learn the respect his parents should have taught him. Even a small child (6 years old) can fire a gun and kill. An 11 year old can be fatal with a knife. I have no intention of being a victim in the morgue. Like I said, the courts will most likely just give probation, a nuisance, but much better than the alternative.
If you can't afford a camera, get a fake one ($10+/-), or throw something together the looks like it could be a security camera. If they believe their actions will come back to haunt them, no way to lie about it...