Fozzie is really amazing with kids. I don't think I've ever seen a dog who is so kid-friendly, and gentle, and patient. He's a Corgi mix. As far as I've experienced, Corgis tend to be very good with polite children... as long as they are properly trained, exercised, and socialized. Any herding breed can and will nip/herd running children, if they're allowed, and if the behavior isn't immediately "nipped" in the bud. ; )
Lots of dogs of individual breeds can be great with children. I would recommend first narrowing down what breeds of dogs would really fit your lifestyle in general, and then decide which breed tends to be most kid-friendly. Dogs who are patient, soft-mouthed, and have a high pain threshold/high tolerance usually make the best kid dogs.