I'd actually not recommend smaller dog personally, I find medium to larger dogs are often more able to handle the sometimes rougher handling of a young one. First one that pops to mind for me at the moment are golden retrievers, often wonderful around other pets and small children, but still need exercise and activity (as would any dog really). In my experience they are oftentimes a bit more mellow than labs. ANY breed can be wonderful with kids really (including rotties and pitties). If you look for an adult dog I'd make sure the dog had experience around kids and was known to be loving and tolerant around them.