Children's encyclopaedia for a 4 year old boy?

[pops]

His questions are driving me mad. Even if I can answer them he asks a supplementary question looking for more detail. I need some answers and thought we could read a children's encyclopaedia together. Can you recommend a good one?

Pops, we have the Dorling Kindersly illustrated dictionary, I'm sure they do an encyclopedia too.

the book people have got quite a few, at ok prices. We've got a box of eight little usbourne ones, loads of pictures in them. They kept me amused for hours anyway!