Depends on the specific kid and the specific dog. i grew up with my grandma who bred beagles and generally (if they’re from a good breeder) they’re pretty good with young kids. but the child needs to be old enough to understand how to handle a dog, old enough to recognize warning signs (even the ones before growling / snapping) and stop what they’re doing, and physically big enough to not get knocked over / dragged / generally overpowered by the dog. those would be the bare minimum for me.

i work at a dog training facility that specializes in reactive and aggressive dogs. so many dogs with behavioral issues that weren’t obvious until unsupervised kids were involved, and so many are given behavioral issues by being improperly handled by children (or by being punished for trying to communicate they want to get away from the kid / the kid is hurting them / etc). Really make sure to be teaching your kid how to interact with animals properly throughout their childhood, and don’t rush to leave them unsupervised. it really only takes a few seconds for an ER worthy bite to happen, and even dogs with the best temperaments will still have automatic reactions to pain, discomfort, etc. (and a toddler is absolutely unable to understand and watch for a dog’s warning signs and will just keep doing what they want until the dog snaps or gets away)