Dirty Bertie by Alan MacDonald and David Roberts.

If your child isn't keen on reading, the prospect of reading about pants, poo, worms, bogeys and all manner of gross stuff that kids love, might be enough to tip the balance. One of my kids didn't pick up a book for pleasure until he was seven.
It's tough for him, he lives in a house with four bibliophiles, and can't understand why we all take such pleasure in reading. In his mind, this in an activity that's tough, not something to relax with. However, he'll make an exception for Roald Dahl and Dirty Bertie. I nearly cried when I went into his room to turn off his light and found him in bed reading a Dirty Bertie by himself.
Dirty Bertie is a boy full of disgusting habit's and fun, much like most children that age, and what's more, Alan MacDonald has written loads of these books.
If you're interested in the whole series, you can find more information here: www.dirtybertiebooks.co.uk
On the front page of the website is a charming stinky sounds game where you can drag and drop sounds onto a score to create a pongy soundtrack, it's totally gross, but kids just love it.