I'm not sure if it's been mentioned but an important factor was that Mance had no scouts out since he'd lost too many to the Others. That's what made the ambush possible at all just like Tyrion's savage friends made Tywin's attack possible.
Not children, maybe pets as some have said. It would be really fun to have a golden furred, green eyed grumpy looking cat named Tywin. And if I ever get a tarantula (when it snows in Dorne) I promise I'll call it Varys.