What do you suggest if my son (13) has a slightly elevated rdw (14.8%) and a slightly low mchc reading (32.5%) - meaning?

Hard to say: Without the context of other lab values, these isolated numbers from a CBC cannot be interpreted. Also, isolated lab values mean nothing by themselves - they are just one tiny clue in a picture of your total health. Don't treat numbers, treat people. Everything has to be taken in context, and commenting on these numbers out of context would be a disservice to you and your son.