Our kids have had great fun with language silliness in the following two books. The King Who Rained is a book of homonyms taking common phrases (some of them less common now than when the book was published in 1960) and making a silly cartoon based on a homonym of one of the words, or the phrase itself. Written and illustrated by Fred Gwynne, of Herman Munster fame, with fun, kitschy illustrations.
Some of the pages use homophones instead of homonyms but are equally delightful.
Eats, Shoots and Leaves is a children's picture book based on the adult bestseller of the same name. With each page showing what can go wrong when commas are misplaced, or not placed at all, kids will howl with laughter at some of the depictions including the gun-toting panda made popular on the adult bookcover.
The illustrations are rather cartoonish, but do a very effective and silly job of exploring the difference a comma can make.
In searching Amazon for links on these books, I found a list of other books that have fun playing with language. What a fun way for kids to explore (and learn!) word usage and grammar!