In the year or so before permanent teeth begin to arrive, you really want to try and get the neighborhood cleaned up and fluoridated better.
Thankfully, our teeth get a second round, but don't think just because there are baby teeth in there, that it doesn't matter. Decaying germs will migrate around the mouth, and settle into the big deep grooves on the back teeth that will be even harder to clean than the ones he currently has.
Put those fires out, either with fillings or extractions.