My grandma ended up with a German Shepherd mix. My 2-year-old loved that dog, and the dog was always very patient with him. One day my son was riding his tricycle, and the dog rushed him (from the other side of the room). The dog was ticked, hackles up and everything. He knocked my son off the trike and bit the side of his face. He had dark red blood drizzling from his eye and dripping off his chin, and little holes all over his forehead and temple where the other teeth hit. He still has the scar just under his eye. 1/4 of an inch up and it would have been his eye ball.
The dog was euthanize.
We decided that there was no way to know what triggered the attack, and it is next to impossible to find a home that is truly child free. I mean, sure, the person might not have kids at the moment - but they might later, or grandkids, or a friend's kids, or the dog might get out...
If I was in your situation, I would get rid of the dogs. I wouldn't make the back-yard dogs. Kids learn to open doors, and they are curious. I know you love the dogs, but their behavior isn't acceptable. There is a fine line between what your dog did, and what can seriously injure a little kid.