Bats
Leo has been feeling unwell, and spent last night awake. Doyle made a clever observation about this the next morning.
Daddy: Mummy and Leo were awake last night, did you hear them?
Doyle: They are asleep in the morning.
Daddy: Yes, they are asleep this morning because they were awake last night.
Doyle: Maybe Leo and Mummy are bats.