Reply #49: many breed rescue groups don't want to place dogs to families with small children

[Muttocracy]

...often that's due more to the way small children treat dogs than fear of what the dog will do to kids. Many breeds, due to their size, temperament, or energy level, are not good for small children. Also, people with small children often are way too busy to deal with a rescue dog, or if they have other children on the way, suddenly they're too busy or declare the dog not good with kids and it ends up back in rescue. Terriers were bred to be strong, tough dogs. Many herding breeds can be driven nuts by small children.

That particular group's policy is on their website - no kids under 6:
http://www.westierescue.com/faqs.asp#children

Of course, humans have this habit of reproducing so it kids can come along later, but they try to put the rescue dog where things will work out the first time.