I think like any breed, there are good and not so friendly ones. Overall, I think they are one of the better toy breeds for children. They are usually friendly and less likely to snap at kids compared to some other breeds. Typically, they aren't recommended for small kids, because they are so small, and more "breakable" if a small child doesn't know how to respect a little dog. If your kids are gentle with dogs, then they should be just fine.
I typically recommend staying away from breeds like the chihuaha, toy poodles, and many of the terrier breeds as they are less likely to be tolerant of young kids. But again, there are exceptions with any breed, but some general characterizations.
A Calvalier King Charles Spaniel is another small breed dog that is great with little ones.