Ask young kids what they want most in a book and the majority say they want it to be funny. You can find books for all reading levels, including early readers, again from Erica, a list with short reviews of 100 of the Funniest Chapter Books for Kids.
How about adding some Dr. Seuss notes to your kid's lunchbox? Jenae from I Can Teach My Child has done all the hard work for you, all you need is a printer.
And finally, from Neil Gaiman: