Not really sure that I would say anything, personally. Unless you feel that, in general, he is being neglected or mistreated??
If everything else seems ok, I would not press the issue. This is coming from a mom of 4, who is not ashamed to admit that there have been occasions when we come home from a night of hockey, dance and lacrosse at 8:30... and bath time is neglected. Not regularly, but once in a while. I am sure my children looked a little ragamuffiny the next day! LoL
Some people (kids included) just have thier own "odor" which can take some getting used to, if that makes any sense.