Glasgow libraries have a reading challange on over the summer again. There is a pre school age one and then an older kids one. Get stickers/card things for each book and then a wee prize at the end. And an over all prize for the child that reads the most books.
If you don't have a card/can't find it then don't worry they are always happy to help. They are desperate for people to sign up...more that sign up = proof of use which means more funding and keeping our libraries open.
I take the kids regularly and if you ask for the fun folder you can do colouring/word searches etc. Great way to spend an afternoon if it's rainy in the holidays.
Plus you can then plonk them in front of the tv guilt free as have don't something educational 
Most areas probably have similar