Measles is hugely scary. Not for kids your son's age (he's "prime health" category), as long as you keep the fever down he probably won't go blind, suffer brain damage, or die (the 3 most common side effects from getting measles). But for infants, young children, the elderly and ANYONE on immune suppressing drug or with compromised immune systems (cancer patients, anyone who has ever had a transplant, etc.)... those "big three" are common, as of course, the many many miscarriages and birth defects caused by it when pregnant women are exposed.
IF he has measles, he needs to be in an isolation area in the hospital, or in isolation at home (depending on what his doctors recommend), as does the rest of your family, and EVERY person he's had contact with in the past 10 days needs to be notified by public health. Otherwise he, and you, can be at risk for the deaths caused, and lives ruined, by his exposing others. It's like knowingly infecting people with AIDs, but worse, because so many will die in 20 days, instead of in 20 years. You DON'T play with measles.
He needs to IMMEDIATELY be seen if you suspect measles. Now.