I heard something similar to what Bathsheba posted - when they're quite young, it's not how much their teeth get brushed that matters as much as what they're eating. Apparently kids who have candy more than once a week have much higher rates of decay, regardless of how often their teeth are scrubbed. I'd keep up with the brushing, if you can, and let him play with the tooth brush too, but make sure that he's eating well. I've heard pieces of cheese are good for cleaning off teeth, and creating a healthy mouth environment. (encourages lots of saliva, which cleans the mouth or something like that?)