I'm a huge fan of the Oliver Moon books! I have a six year old boy who is a good reader for his age and so I was looking for chapter books that weren't too difficult to read and that were easy to understand.
For the uninitiated, Oliver Moon is a young wizard at Magic School and the books are all about the magical mayhem that he gets up to. In this book Oliver is chosen to look after Nippy the nipperbat, the class pet. Of course, things don't go at all according to plan and poor Nippy ends up lost thanks to Oliver's little sister, the Witch Baby. Oliver then tries to put things right by getting a new nipperbat called Norris...who turns out to be nothing like Nippy! Norris loves singing naughty little songs, and his songs and antics had my boys in fits of laughter. Of course, you'll be glad to know that there's a happy ending for everyone. :)
These books have really hit the nail on the head! They are full of lovely humour that five years plus can easily understand and appreciate, and have lovely, short chapters that are brilliant for giving a real sense of accomplishment to a reader who's embarking on "proper" books for the first time. I think that one of the nice things about Oliver is that it is really easy for a young child at school to identify with many of his experiences. The book has simple little black and white illustrations throughout that add nicely to the story.
I would highly recommend the Oliver Moon series for any budding readers that are ready for short chapter books, or indeed as fun, light reading for more accomplished readers.