Interview Puzzles :: Discussion

A mother tells her two children, a boy, and a girl, to play without getting dirty.

However, while playing, both children get mud on their foreheads.

The mother says At least one of you has a muddy forehead. She then asks the children to answer Yes or No to the question: Do you know whether you have a muddy forehead?

The mother asks this question twice.

What will the children answer each time this question is asked, assuming that a child can see whether his/her sibling has a muddy forehead, but cannot see his or her own forehead? Assume that both children are honest and that the children answer each question simultaneously.