Overall, 16 percent of boys and 22 percent of girls in the UK study admitted to ever smoking.

In a 2009 survey on risky behaviors by the U.S. Centers for Disease Control and Prevention, 10 percent of American high school students admitted to having tried smoking a cigarette before age 13. Among 8th graders, between 30 and 60 percent (depending on the state) said they had had “more than a few sips” of alcohol.

Figuring out which children are most likely to drink and smoke at a very early age is important, according to Melotti, because the earlier the start, the greater the risk of lasting problems.

“Drinking at an early age,” he said, “has been related to a series of adverse outcomes, including the risk of developing alcohol-use disorders in later life.”

SOURCE: Pediatrics, online March 14, 2011.