I ordered these books for my colleague and they are sitting beside my yet-to-review-artbooks box.

They are distracting me from my art books because they are a real joy to read. Funny and educational. They are for kids, probably around 7-12.

There are quite a lot of volumes from the Horrible Science series. There's also the Horrible Histories series.

The books are available individually as well as in a box set. The box set is more economical, not to mention if you're ordering from overseas you just have to pay one per-item shipping charge.

Horrible Science availability:
Amazon (US | CA | UK | DE | FR | IT | JP) and Book Depository (US | UK)

Horrible Histories availability:
Amazon: US | CA | UK | DE | FR | IT | JP) and Book Depository (US | UK)