These books make maths interesting. Some kids love them and reread over and over again, some don't like them so much. Try one and see if your kid takes to this format and humour. You can also check out their wesbite http://www.murderousmaths.co.uk/. 

Find out about how maths could help you rescue someone in deadly peril, how not to shoot yourself with a cannon, and meet famous mathematicians who were really hard. And watch out for One Finger Jimmy, Chainsaw Charlie and their gangster friends, who are living proof that maths can be murderous.