Knock-Knock

Colt and Skyler think they are hilarious. They make up knock-knock jokes until I finally tell them to stop; the problem is they, of course, aren't funny but they insist I laugh and laugh. It's hard to fake laugh for very long. Here are some of the jokes I woke up to this morning:

Colt: "Knock, Knock" (who's there?) "Red" (red who?) "Red Rocket!"

Skyler : "Knock, Knock" (who's there?) "Green, Blue, Strawberry, and Green" (green, blue, strawberry and green who?) "Dad!"

I have tried telling some funny ones so they understand how this goes but it hasn't helped yet.