My eldest has disgusting teeth. He has lots of decay, no matter what we do. Skybie is right, some kids just do have cruddy teeth! We brush his (he is 7 and we still do them for him) twice daily, he has a tooth moose, and still they are grose! My other 2, we brush twice daily and theirs look fine so far. Poor DS1 has had a tooth pulled out cos it fell apart after having a crown put on it, and he has had multiple fillings. It SUCKS!

Just try to make sure you brush every day twice, if not 3 times if you know he has bad teeth.