Hey kid who made this thread.
I wasn't gonna reply but.. I was in the EXACT same situation as you about 3 years ago. I was walking my dog, a kid did the EXACT same thing that happened to you [he taunted my dog, threw stuff at it]. My dog decided to chase it and bite his leg, and made him bleed... not as much as yours though from what you said your kid bled a lot. My dog put a big scratch on the kid's leg. His mom came out and threatned to sue me.. I said 'cool, go for it' and asked if she wanted my name/number/home adress just to piss her off.
She went back in, and I never heard from her since.
My advice to you: Sleep on it little boy, I highly dought that someone will sue you over such a small thing, trust me, suing someone is not as easy as you think, you need lawyers, legal papers, have to take time off work etc. It's a pain in the ass, and with doing all this you have to remember you might not win.
Peace.