1. Watch out if your dog uses his mouth in play or to move or control the child. Any dog over 5 months of age should not be using his mouth to play, and is probably not playing, but actually trying to control or dominate humans with his teeth, no matter how gentle your dog appears to be.
2. Watch out if your dog cuts in between you and your child during hugging or engaging in any affectionate interactions. This can indicate jealousy, or rank aggression, or guarding of you, the owner.
3. “Let sleeping dogs lie” is a saying created by someone who really knew dogs. Teach and NEVER allow your children, (or visiting children), to startle, awaken or hug a sleeping dog. Also, dogs by nature are grouchier and testier at night, or in the evenings, and if your dog drops off into a heavy sleep in the evenings, put him away in another private room, or encourage him into a crate, so that you can prevent the possibility of a child startling or waking the dog.
4. Watch for any growling, whether in play or not. Dogs never growl for any other reason except to warn us of biting. So often owners have commented that their dog growled all the time, and were shocked when it finally bit someone, having believed that the growling meant the dog would never bite. Growling is never a vocalization a dog makes just to “talk”, although some breeders of certain breeds have mythology that their breed “talks”, commonly Rottweilers. Dogs don’t “talk” by growling – they growl to let us know that they need help, as they are warning us they would like to bite.
5. Watch for combinations of events: i.e. your dog may be fine if approached by your child while chewing on a rawhide, and separately, your dog may be fine when approached and hugged while resting on your couch, but your dog may growl or even bite when approached by your child AND hugged WHILE he lies on the couch chewing a bone. I.e. your dog may be fine being hugged by your child in general, and your dog may be fine when held by the collar and restrained from chasing the family or cat or bolting out the front door, but your dog may growl, snap or bite when hugged WHILE being restrained or keyed up or frustrated.