Before answering this question, it is very important to note that any dog can bite a child and the safest precaution to take is not to leave children alone with dogs. Having said that, from historical evidence it is suggested that some breeds show a tendancy to have more patience than others when it comes to children.
Golden Retriever or Labrador Retriever are two dog breeds that display the highest level of patience were children are concerned and would never disturb your children unnecessarily. Golden Retrievers are considered better than Labradors but require more looking after because of their longer coats. They also have a soft mouth resulting in a softer bite.
Other breeds of dogs to consider are the Pug, Bernese Mountain Dog, English Bulldog, Bearded Collie, Boxer, Portuguese Water Dog, English Shepherd, Newfoundland, Sussex Spaniel, Old English Sheepdog, Standard Poodle, Boston Terrier, and St. Bernard.
If choosing a dog from reputable Kennels, always ask if you can meet with the parents of a litter and try to ascertain their behaviour. Research is key when buying a dog that will be around children as indeed is proper training.
Consider having your dog spayed or neutered because this can eradicate some of the aggressive behaviours in the dog. This does not guarantee that your children would be safe with the dog but at the very least will help minimise the risk. Also, get a dog that is social and enjoys being playful with your children. Last but not least, take your puppy/dog to the Vet to get regular vaccines.