Tell him a joke when he's a baby !
Swim down and knock on the hatch. (In Sweden we have a running tradition of telling jokes about stupid norwegians. They do the same about swedes)
You tell her that her smile is contagious.
Because she was a-Kraid to. Now I think about it, this joke is a bit more "Riddle-y," than say an actual joke.
The punchline is too long.
Babies
A: Miscarriage This joke never gets old, just like the baby.