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.