More kids and teens are smoking marijuana at younger ages, according to data collected by the National Survey on Drug Use and Health. From 2008 to 2009, there was a 9 percent increase – to 7.3 percent of people age 12 or older – who currently use marijuana. During the same time period, the average age of first-time marijuana users decreased to 17 years old.

The human brain is still developing throughout the teen years and in to a person’s 20s That’s why the Office of Drug Control Policy says using marijuana at the age of 12 can lead to addiction, respiratory illness, weakened motor skills, and cognitive impairment not only while the child smokes but for years after a person quits.

Gil Kerlikowske, director of National Drug Policy, says parents need to know why marijuana use early in a child’s life can be dangerous.

“We recognize American families are facing many challenges today, but failing to adequately prevent young people from using drugs now can lead to a lifetime of devastating consequences,” said Kerlikowske in a press release announcing the data.

Proponents of the legalization of marijuana have jumped on the survey’s findings. The Marijuana Policy Project released a statement in response to Kerlikowske’s comments, suggesting that the data demonstrate that legalizing the drug could curb the trend of more young people becoming marijuana users.

“Unlike alcohol and tobacco – which are sold by licensed, tax-paying vendors who are required to check customer ID – marijuana use continues to increase among young people largely because it is sold in an uncontrolled, unregulated criminal market by drug dealers who are perfectly happy to sell to minors,” said Steve Fox, with the Marijuana Policy Project, in a statement.

The Office of National Drug Control Policy says parents concerned about whether their child is using marijuana should begin following three steps to insure their children stay drug-free. Kerlikowske said parents need to know the risk factors associated with marijuana use, be able to talk with their children about drug use, and regularly clean out their medicine cabinets so old, unused medicines are thrown away and not abused.

-CNN Caitlin Hagan