A Home Office survey found that some drug users had admitted taking ecstasy when they were just seven years old, while others said they smoked cannabis at age eight. The youngest reported user of cocaine was just nine.
It is the first time that the crime survey report included the lowest ages at which respondents said they had tried the three most commonly taken banned substances.
Detailed figures showed that almost a third of young people and adults who had ever taken cannabis, now a Class B drug, first tried it when they were under 16.
By the same age, when buying alcohol and cigarettes is still illegal, 6 per cent of those who had ever taken Class A powder cocaine had tried it.
Of all those who had ever taken ecstasy pills, classified as Class A, 8.2 per cent had done so before their 16th birthday.
Analysis of drug misuse in the 2011-12 Crime Survey for England and Wales, published on Thursday, said: "The most commonly reported age for first taking cannabis was 16 years. But, as expected, there was a lot of variation among adults in the age cannabis was reported to be first taken, ranging from eight to 56 years old (with an overall average of around 18 years).
"Age of onset was most commonly 18 for cocaine powder, but again this was within a wide range of reported ages, from nine to 57 years old (the average reported age of onset was about 21 years).
"The most commonly reported age of onset for ecstasy was 18 years. Again, the first age of use reported by adults varied considerably, between seven and 51 years old (with an average of around 20 years for age of onset)."
However although some survey respondents claimed to have taken narcotics while very young, in general drug misuse continues to decline.
The proportion of adults aged between 16 and 59 who had used an illicit drug in the past year stood at 8.9 per cent, "around the lowest level since measurement began in 1996". Drug-taking among young people aged 16 to 24 has also fallen.
Over the past decade there has been a "notable decline" in cannabis use along with a smaller fall in use of ecstasy, and a recent drop in cocaine use. Amphetamines have fallen "markedly" out of favour since the 1990s.
Even the popularity of new highs such as mephedrone, known as meow meow, appears to be on the wane with 3.3 per cent of young people taking it in the past year, compared with 4.4 per cent in 2010-11.
Separate figures also suggested that are becoming healthier. An NHS study found that drug-taking among secondary school pupils had fallen by 12 per cent over the past decade.
A quarter of 11 to 15-year-olds had ever tried a cigarette, the lowest proportion since the survey across England began in 1982.
Jeremy Todd, chief executive of the charity Family Lives, added: "Whilst news that the number of schoolchildren taking illegal drugs, smoking and drinking alcohol has declined, many parents will still be struggling when their teenager begins to experiment.
"We speak to thousands of families every year and evidence shows that parents are the main influence on how children approach drugs and alcohol.
"Equipping parents with the tools to ensure they can talk effectively with their children is the best way of preventing children experimenting at an early age and can prevent later problems in teenage and adult life."