Diary of a Worm. by Doreen Cronin, with pictures by Harry Bliss (2003), is an all time classic!
It will always be loved by kids and their lucky parents. It is written in the first person--in the words of an intelligent worm child--and it describes things that happen to him in his daily life as a worm. He plays with his friend, Spider, he describes some of the dangers of worm life, like hopscotch, and he goes to school. Once he forgot to bring his lunch, so he ate his homework! His teacher told him to write "I will not eat my homework" ten times, but when he was finished he ate that too.
You will never look at worms in the same way after reading this book. Worms are good for the earth, and worms (at least in this book) are funny!
In my book rating system, this rates an A+ ! I recommend this book for ages 3 to 8. There are two sequels--Diary of a Spider, and Diary of a Fly (but not Diary of a Wimpy Kid! That's another story...)