Help with newborn puppies!?

there are only two. it seems like one(girl) is constantly eating, and the other(boy) only eats a couple times a day. also, the girl seems to cry more and the boy is the runt. what could be the cause of such different eating habits? do you think that the girl is eating too much or the boy isnt eating enough? they are only 4 days old! is any of this reason for concern? please help me.