hmm it is a tough one and I'm another mummy who tends to 'forget' to brush his teeth.. Ummm we sing songs about brushing teeth (just what ever you want to make up. We sing part of the brush, brush song that used to be on playhouse disney. "do the brush, brush, brush, whooaaa, do the brush, brush, brush, whoooaaa. If you want to smile like a crocodile, if you want to laugh like a tall giraffe, to the left and to the right every morning, every night.. etc etc), and also we get him to have a go at brushing our teeth, then we have a go with brushing his teeth (separate toothbrushes of course). He is very independent though and doesn't really like help, so it is sometimes a struggle to get them brushed.