Why does my dog bite kids' toes?

My dog is a bit odd. I've mentioned that he is a social eater (he waits to eat when we or the kids sit down to eat).

Well he has another odd habit -- he bites kids toes. Not hard, but more nips at them. And usually this is when he is eating and they are sitting at the kitchen table eating. He will run under the table and nip their toes and then go run and grab a bite (of his food that is). And if they are not sitting at the table - he will come run at them and nip their toe where they are standing.

Now why in the heck does he do this? He only does it to kids - not just our kids, but we have other kids over. He doesn't do this to any adults.