I think a large portion of the issue here is a lack of control by the owner. To have your dog get out of the house once is a mistake. To have it “Nip” someone, which in my opinion drawing blood is stretching the term “Nip” a bit is another. But for them to get out again when it is the animal control officer at your door is worse yet. If this was the child’s fault that the door was opened then that is still the adults fault, as we are responsible for the actions of our children and our pets. As much as I agree, if it had been most other breeds, it would not have been a huge issue. I guess it also depends on the definition of a nip.

Do you praise him when he goes outside? Also is he giving any indication of having to go back out? I would recommend taking him back out about ten minutes after he comes in, and then if he goes outside, praise him a lot.  Hope this helps.