
Firstly, sorry to hear about the problems you are having with your rescue dog. It's very difficult, almost impossible to give advice on temperament issues over the internet - particularly when biting is involved. There could be so many reasons for this behaviour and without someone being able to assess the dog personally it could be dangerous to attempt to offer advice or even second guess as to why he is behaving this way.
Get back on to the shelter where you got him from and see if they can provide more info on his background before they took him on and also advise on his temperament as assessed by them. It seems irresponsible that they would knowingly allow a dog with the propensity to bite to go to a family home :-( but then again perhaps this behaviour was not in evidence then.
You don't specify how long you've had the dog - he may have developed a health problem that needs treatment by a vet. Please provide some more specific info if at all possible in case anyone can be of more assistance in the interim but I'd strongly recommend that you seek professional advice from the shelter and a vet a.s.a.p. before trying to tackle this issue. In the interests of safety meantime, he should be kept away from your children.
Good luck, HTH, Teri :)