A government survey of teens done from 2002 to 2006 said slightly more than half had engaged in underage drinking.
Asked about the source of alcohol, 40 percent they had gotten it from an adult for free over the previous month, the survey said. Of those, about one-in-four said they had obtained it from an unrelated adult, one-in-16 from a parent or guardian, and one-in-12 from another adult family member.
Roughly 4 percent reported taking the alcohol from their own home.
"In far too many instances, parents directly enable their children's underage drinking - in essence, encouraging them to risk their health and well-being," said acting Surgeon General Steven K. Galson. "Proper parental guidance alone may not be the complete solution to this devastating public health problem - but it is a critical part."
Not only that, pointed out CBS News legal analyst Lisa Bloom on The Early Show Thursday, "parents can be looking at criminal as well as civil liability (if they give their kids alcohol). Translation -- jail time, money damages to victims of teen drunk driving, paying for their medical costs, even punitive damages.
"If parents knew they had a ticking time bomb, if they knew they had a kid who was a danger, and they give that kid alcohol, they give that kid a car, the kid goes out and causes an injury to somebody, parents can lose their home. We're talking about dire consequences."
Bloom says that also applies to parites held without parents' knowledge in their homes: "They would be liable. Parents are responsible to know what's going on in their homes. Parents are responsible to keep their kids away from alcohol, because parents are in the best position to know. Parents are in the best position to protect the rest of us from teen drunk drivers. And many have had a rude awakening the next day, after those parties, to find that social host laws now apply to them."
What about parents who say they would prefer to provide alochol to their kids, so they'll know what and how much the kids are drinking, and because the kids would just drink, anyway, away from home?
"They're not gonna drink, anyway. Kids of parents who are heavy drinkers are three-times as likely to become heavy drinkers themselves. Kids of parents who abtain are much more likely to abstain. We, as parents, don't think we have an influence on our kids, but we do."
The nationwide study by the Substance Abuse and Mental Health Services Administration, released Thursday, tracks the social contexts involved in underage drinking, a problem leading to thousands of alcohol-related traffic deaths and injuries each year.
About one-out-of-five of those aged 12-to-20 - or roughly 7.2 million people - said they had taken part in binge drinking, defined as consuming five or more drinks on at least one occasion in the past month, the survey said. Rates were significantly higher if they lived with a parent who engaged in binge drinking.
The study, which uses data from the National Surveys on Drug Use and Health, is based on a scientific random sample of 158,000 people aged 12 to 20 in the United States.
Among the findings:
"This report provides unprecedented insight into the social context of this public health problem and shows that it cuts across many different parts of our community," said Terry Cline, administrator of SAMHSA. "Its findings strongly indicate that parents and other adults can play an important role in helping influence - for better or for worse - young people's behavior with regard to underage drinking."