Choosing a dog with the right temperament is extremely important, especially if you have children in the home. Some breeds are well known as child-unfriendly, and they aren't necessarily all big dogs. Small terriers and spaniels are not well regarded as pets if you have kids. Neither are poodles, chow chows, pinschers and schnauzers.
Conversely, some of the larger dogs can be the most gentle with kids. Retrievers are legendary for their temperament, and make great family dogs if they're well exercised. You can also add boxers, mastiffs, hound dogs, collies and St. Bernards to the list of dogs suited for kids. Whatever kind of breed you get, be sure to spend lots of time socializing them and making sure they can be trusted around your children -- and that your children can be trusted around them.