S.L.
I think you have some great advice here re. small claims court so I won't repeat it. The other moms are correct in saying that you may not see a dime even if you are awarded a judgment, but I would not let that stop me.
You are not unethical or "sue happy" if you use the court system to right a wrong that has been done to you. That is why the system is there and why it is called "tort" (French for "wrong") law. Unfortunately in our society, there is a small percentage of people who are a) clueless; b) bullies or c) both. Tort law exists, in my opinion, to gently or not so gently persuade these people to do the right thing when they have wronged someone else.
I might try a slightly more devious route before small claims court. I might re-visit them with a copy of the vet bill and tell them that you are concerned for their dog. If it becomes a matter of public record--through a court case--that this is a malicious dog, and there is another incident, animal control might take their dog and euthanize it. If this is a one-time occurence and they can make sure the dog is secured, plus reimburse you, I would tell them I won't file a report. Maybe this will have some effect...
PS I hope your dog is OK and that kids in the area are safe from this dog! I think secure fencing is almost as important here as getting reimbursed!