So keep talking with them. Sexual fantasies about family members of both genders are common, too. Kids may find these thoughts upsetting. We must reassure them that just dreaming or thinking about things doesn't make them happen. Boys worry about their penis size.
Girls worry about their breast size.
Reassure them that no two people are the same. But we must also encourage them to think for themselves. Kids are fascinated with the way their bodies change. It's common for them to look at and touch each other's sex organs. This is one of the ways they learn that they are normal.