Quick summary. I have two DS 7 & 9 and A 1 year old collie lurcher cross who has been with us since a pup. He gets plenty of exercise, and socialization at doggy day care and we do training. Lots of cuddles and attention from my ds. However, in the last couple of weeks he has snapped at kids he knows, my niece who walks him sometimes, my ds, and a neighbour kid who went to pet him today. It wasn't just a warning snap either. He made contact but did not break skin. He gave no warning and was lightening fast. Please please advice the best course of action. Thanks you