Welcome to Ask Dr. Harvey Karp, our new fatherhood advice column at Esquire, where the author of The Happiest Baby on the Block and creator of the SNOO answers your burning questions about parenting.

Q: Potty training advice needed: Our son just turned 3. He's great with peeing, except he still wears diapers for sleeping. We are struggling with pooping. He knows he's supposed to go in the potty.

The source of their distress? A small child who is trying to learn how to poop like a member of modern society. Ask any parent who has had to do multiple loads of particularly unpleasant laundry, or ...