I have to agree with Jerseygirl, though I feel that some breeds should probably be avoided. My neighbor's chihuahuas are insanely eager to catch them, though would probably not know what to do if they caught one, I still am grateful that the one time they escaped taught her to be VERY careful. (I give her eggs every week after all). All that chasing isn't good for anyone!
Whatever breed you get, go for calm, gentle temperament for the good of both your kids and your chickens. If they are taught from day one that the chickens are not flappy squawky squeaky toys, but something to be nice to and protect, not chase, not play with, not bother at ALL... most dogs can learn.
We had a German Shepherd that eyed the chickens a LOT, but never acted on it... well, he sort of rushed "through" them just for fun every once in a while, but he knew not to snap at them. We had a Cocker Spaniel that was gentle as a lamb never even considering chasing them, but he was an old style 'field trial' type dog, bred for hunting and temperament, not an over-bred show-dog type... I had a most amazing Australian Shepherd, who knew the choocks were part of his flock and kept them away from danger (the river or the road) but he was very very well trained and always pushed slowly, which is VERY different than chasing for those who know herd dogs, and another Aussie/BC mix who was rather nutty but finally learned to just LEAVE them... he was not terribly trustworthy with them, but he learned, and he was the only one who was not totally trustworthy even after lots of work. My mom for a long time had a Pomeranian which I would NEVER have trusted with them, but they didn't have chickens anymore then, and I had a roommate that had a Jack Russel, and I'd say most terrier breeds would be pretty iffy just because they are so determined to GET whatever they think they should GET... iffy, but not impossible. Again, TEMPERAMENT, TEMPERAMENT, TEMPERAMENT!
It took work with them all though, calm, consistent, steady work, Work, WORK!
//edit to add// My SILs Corgi is totally trustworthy too, but when she was younger, she'd have been nearly desperate to herd them... she once tried to herd a small flock of deer! She wanted to herd EVERYTHING!