111 riddles and brainteasers for children and adults. Particularly good in an EFL setting. The language is safe for children.
I usually start off a lesson with a riddle. It can help with behaviour management in general and creates a good rapport between the students and the teacher.
Where I work, students don't use English on a daily basis so this is an enjoyable way to help foster a love for the English language; teaching them to 'play' with the language.