You are generally strictly liable for any damages caused by your dog. Was there any damage to the other dog? Was the other dog off leash? If the other owner does nothing about the fight, then you have nothing to worry about. However, if the other owner does sue you for damages, the fact that his/her dog bit your son is not necessarily in your favor - it would depend on all of the circumstances.
You should notify your homeowners' insurer about the fight now because if you wait, they may refuse to defend the suit or pay the other owner's damages should they decide to sue.
Was the other dog hurt? If the other dog was not harmed then you should not be in trouble. But, if it was hurt, then you can be held legally responsible. I don't see you being in trouble for your son's injury.
(THESE COMMENTS ARE NOT LEGAL ADVICE. They are provided for informational purposes only. Actual legal advice can only be provided after consultation by an attorney licensed in your jurisdiction. Answering this question does not create an attorney-client relationship or otherwise require further consultation.)
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