On average, kids under age 3 catch six to eight colds a year. “We think that since most children are encountering viruses for the first time, their immune systems aren’t able to kill them as quickly as when they encounter them again,” says Carol J. Baker, M.D., a professor of pediatrics at Baylor College of Medicine in Houston. What’s more, because kids aren’t overly concerned about having a runny nose, the virus tends to end up on their hands, clothing, and toys—where it can live for 30 minutes. When another child touches an infected toy and then rubs her nose or eyes, she can catch the cold.