Male or Female??? - Daddy picked them up & looked Underneath

A three-year-old boy went with his
dad to see a new litter of kittens. On
returning home he breathlessly
informed his mother, "There were
two boy kittens and two girl kittens."

"How did you know that?" his mother asked

"Daddy picked them up and looked
underneath," he replied."I think it's
printed on the bottom!"