If this guys your buddy i wouldnt turn him in, **** happens man, especially with 4 year olds, no reason to be causin bad blood. however it does suck that it instantly attacked your dog. If it happens again, shoot his dog, plain and simple, 3 strikes and the *******s done.
I love my neighborhood, we have about 8 dogs, a few ****su's my lahsa, a sheep dog, some goldens and some labs, they all belong to people over 50 save for the sheep and mine, so they're all really tame dogs, they yap at eachother from time to time but no ones ever been bitten in our neighborhood, and when the dogs get up close they just sorta sniff eachother and act half scared.. its pretty amusing.