While brushing the tongue can be helpful, scraping the tongue with a tongue scraper seems to be more effective in reducing VSCs. Mouthrinses are only temporary solutions to the problem. Currently, there are some mouthrinses that claim to alleviate halitosis, but more research needs to be completed to substantiate these claims. Bad breath can also be caused by sinus infections, tonsillar problems, respiratory illnesses, gastrointestinal problems, and other systemic conditions. I am not aware of a relationship between permanent tooth eruption and bad breath.
Some dentists use portable sulfide monitors to diagnose halitosis.
Other dentists argue that these devices are best reserved to chart a patients treatment. The best way to diagnose halitosis is by using your sense of smell. I commend you for your oral hygiene efforts. Hopefully, you are brushing your son's teeth at least twice daily. Flossing will remove bacteria and food debris between teeth.