Chances your child will catch it: 77 percent of children come down with this virus by age 2.
Symptoms: Although the telltale sign is a red rash across the body that can last for a few days, most infected kids simply develop a fever, a cough, and possibly diarrhea. "Many parents don't ever know their child has had roseola," says Philip R. Fischer, MD, medical director of Mayo Eugenio Litta Children's Hospital, in Rochester, Minnesota. "Without the rash, it just seems like a fever or a cold."
Contagious? Your child can infect others until his fever breaks, but the rash itself isn't contagious.
Rx: Treat the fever with ibuprofen (for children 6 months and older) or acetaminophen. Simply ignore the rash, which looks a bit like measles but isn't itchy or painful and will go away on its own.
You need to know: The virus that causes roseola can stay in the body and reactivate, so it's possible your child could get it again.