Nearly half a million children in England and Wales are gambling every week, according to a report.
The Gambling Commission has warned parents and guardians to be vigilant after publishing a report indicating that 450,000 children are gambling regularly, and 9,000 are likely to be problem gamblers.
Some 8% of 11 to 15-year-olds had gambled on a commercial site in the week prior to taking the survey, including betting shops, bingo halls and arcades.
The most popular forms of gambling continue to be fruit machines, placing a private bet with friends and National Lottery scratch cards, typically bought by a parent or guardian.
The poll found 3% of children have spent their own money on online gambling and 6% have gambled online using their parents' accounts, either with or without permission.
The findings indicate that the overall rate of gambling among 11 to 15-year-olds is around 16%, compared with the 5% who have smoked and 8% who have drunk alcohol in the last week, while 6% have taken drugs in the last month.
The overall rate of gambling among the age group has remained relatively static over time as smoking, drinking alcohol and drug-taking has seen a decline, the report said.
The proportion of 12 to 15-year-olds classified as problem gamblers is 0.4%, a similar figure to the previous year.
Gambling in the week prior to taking part in the study was twice as prevalent among boys (21%) than girls (11%).
Three quarters (75%) of 11 to 15-year-olds have seen gambling advertisements on TV and 63% have seen them on social media websites.
Of those surveyed, almost 60% agreed that "gambling is dangerous".
Gambling Commission executive director Tim Miller said: "We're often reminded to discuss the risks of drinking, drugs and smoking with our children.
"However, our research shows that children are twice as likely to gamble than do any of those things.
"We want to reassure parents that our rules require gambling businesses to prevent and tackle under-age gambling and we take firm action where young people are not properly protected.
"We recognise that there are some gambling activities in which young people are legally permitted to partake - such as using a crane machine to win a toy, or betting between friends.
"But we would encourage parents to speak to their children about the risks associated with gambling, so that if they choose to gamble in adulthood, they will do so in a safe and responsible way."