The Gambling Commission study suggests that 450,000 children aged 11 to 16 bet regularly, more than those who have taken drugs, smoked or drunk alcohol.
Bets with friends, slot machines, and scratchcards, were most popular.
A campaigner on the issue, Bishop of St Albans Right Reverend Alan Smith, called it a "generational scandal".
"Today's findings by the Gambling Commission makes worrying reading and serves as a warning to parents," he said.
The Young People and Gambling report found:
- Over the past 12 months, 39% of 11-16 year olds have spent their own money on gambling and 14% in the previous week
- Young people who have gambled in the past week spent an average of £16
- 6% had gambled online using a parent or guardian's account
- 60% of young people think their parents would prefer them not to gamble at all, however only 19% said their parents set strict rules about gambling
Some admitted using betting shops or online gambling sites despite them being illegal for under-18s
The analysis also suggests one in seven boys followed betting brands on social media.