The Wee Free men is the first in a series of Discworld Books for children. That doesn't mean that any of the usual Terry Pratchett humour is lacking, nor is it patronising. It's just slightly more suitable for a younger audience. Which makes it a perfect introduction to the Discworld, where nine year old girls can take on the Queen of Faeries* armed only with a saucepan, a talking frog, Granny Achings Magic Book titled Diseases of Sheep and some Nac Mac Feegles**. Nac Mac Feegles are little blue men (and the occasional woman- the Kilda) who like fighting, drinking, pillaging, but don't like reading or writing due to their fear of Lawyers.
This book really is genuinely funny, with many moments that will make you laugh out loud, so be careful where you read it. If you always thought that fairytales were really rather boring and a bit stupid (who said that the old lady living in the cottage in the wood peacefully minding her own business could only be an evil cackling witch anyway?) then this is the book for you. In fact, even if you rather like fairytales, and think that it is quite obvious why the old lady in the wood is the evil old witch, then you should still give it a try, it might just make you think. It'll certainly make you laugh, which is more than most fairytales manage.
As for why the nine year old Tiffany (our brave and courageous heroine) decides to take on the Queen of the Faeries with only a saucepan, a sheep disease book and some Nac Mac Feegles, you'll just have to read it and find out.
*Pronouced Fairys, but that doesn't mean there isn't a difference
**Alternatively known as The Wee Free Men, just so you don't get confused.