More than 120 children under the age of 12 in Wales were referred for specialist help for drug and alcohol problems, figures reveal.
They include 66 cases of alcohol abuse, 13 of cannabis use and 17 of heroin use.
Dr Andrew Dearden, British Medical Association in Wales chairman, said the figures for 2008-09 were "shocking".
Wales' chief medical officer said work was under way to raise awareness about the damage drugs and alcohol can cause.
The assembly government figures show that 126 children were referred by their GPs for specialist substance misuse help.
But Dr Dearden, who has a surgery in Cardiff, said he feared the figures were "the tip of the iceberg" as they only included those who had been to see a doctor.
He said the youngest person he had referred for alcohol help had been aged around 16.
"These figures are only those we are aware of - it's frightening," he said.
"If you go back 15 to 20 years this wouldn't have been happening."
He said he believed several "society factors" were behind the figures - and that it would take a "multi-pronged" approach to try to deal with them.
"Drugs and alcohol are becoming more socially acceptable and kids want to be adults sooner these days," he said.
"Also they are much more available than they were. Then we get the role models on TV and other places. And another factor is family influence. The more children see their parents doing it, the more they think it's acceptable.
"These figures should be causing all of us major concern.
"And as there are so many factors contributing to the number of children drinking alcohol and using drugs, equally there will have to be a multi-factorial approach to deal with the issue - there's no simple solution.
"Education and schools can only do so much - parents need to be thinking about the example they're setting.
"And while the law in itself isn't going to fix things, it could help by cracking down on things like the advertising of alcohol."
Chief Medical Officer for Wales Dr Tony Jewell said the figures were "worrying" and that the assembly government was working to reduce the numbers.
"We continue to place emphasis on raising awareness amongst children and young people about the harmful use of alcohol and drugs, and the damage that substance misuse can cause to people's health, families and the wider community," he said.
"This is why we have provided Community Safety Partnerships with an additional £3m per annum from 2010-11 to specifically develop and expand substance misuse treatment services for children and young people.
"We have also provided funding to the Strengthening Families Programme which helps parents and their children understand the harms of drugs and alcohol.
"We also fund Dan 24/7, a helpline which provides free, bilingual and confidential information or help to anyone in Wales relating to drugs or alcohol."