Links to online gambling firms have been placed in junior sections of the websites of 15 football clubs, a BBC investigation has found.
The logos, linking to gambling sites, often appeared under details of how to join junior clubs and be a club mascot.
The Advertising Standards Authority (ASA) demanded "immediate action" in response to the BBC's findings.
The English Football League apologised, while some of the clubs have removed the adverts from their junior sections.
ASA rules state online gambling adverts cannot be targeted at anyone under the age of 18.
However, 5 live Investigates discovered 15 football clubs spanning the Premier League, the Championship, League One and the Scottish Premiership, had logos of betting firms or links to gambling sites on pages aimed at junior supporters.
All of the clubs have gambling firms as their shirt sponsors.
Among them was Premier League side Wolverhampton Wanderers, whose "Junior Fans" page contained the logo of a gambling company and club sponsor at the bottom of the page.
The link opened a page of a gambling site featuring Wolves players.
Championship club Aston Villa's "Junior Villans" page contained two logos of gambling firms, including one which opened an "Ant and Dec's Saturday Night Takeaway" game and a "Jurassic World" game.
Scottish Premiership champions Glasgow Celtic's "Young Hoops" pages also contained links to a gambling site.
All three clubs have since removed the adverts from their pages.
It comes after NHS England this week warned football clubs should do more to help tackle gambling addiction.
Which clubs carried gambling links?
Premier League: Wolverhampton Wanderers
Championship: Aston Villa • Blackburn Rovers • Bolton Wanderers • Brentford • Ipswich Town • Norwich City • Nottingham Forest • Stoke City
League One: Blackpool • Bristol Rovers • Charlton Athletic
Scottish Premiership: Glasgow Celtic • Hibernian • Motherwell
Shabnum Mustapha, from the ASA, said clubs needed to take "immediate action" to remove gambling logos from junior pages.
"Our compliance team will be writing to the Premier League, English Football League, the FA and SFA to set out clearly our concerns in this area, to highlight the UK gambling rules and how they apply to football club websites."
Tim Miller, executive director of the Gambling Commission, said it was "not acceptable" for gambling advertising and logos to be presented on web pages of sports teams that are targeted at children.
"Sports teams should be ensuring that all content on such web pages is appropriate for children and we expect gambling companies to take responsibility for where their adverts and logos appear."
Anne Longfield, the Children's Commissioner for England, described the findings as "hugely surprising".
"That's not something I would have thought would have been the kind of site that you'd want your seven, eight, nine-year-old child to be going through to," she said.
Ms Longfield called for education about gambling to be included in the school curriculum.
Last November, 24-year-old Jack Ritchie, from Sheffield, took his own life after battling a gambling addiction, which began when he was 17.
His mother, Liz, who has since founded the Gambling with Lives campaign group, said she was sure betting adverts in football had affected him.
"It normalised it and it's made normal by being a part of the thing they love, which is football," she said.
Both Wolverhampton Wanderers and Aston Villa said they had removed the logos from the junior sections of their websites, while Glasgow Celtic said the club would "never intentionally promote such services to those under 18".
However, fellow Scottish Premiership side Hibernian said its "Hibs Kids" website was designed for "parents and other adults, not directly to children".
Shaun Harvey - chief executive of the English Football League which represents the 72 English clubs outside the Premier League - said: "We apologise to all supporters of our clubs for any concerns this may have raised.
"All clubs who have betting partners have been instructed to remove any logos from pages aimed at minors."
Mr Harvey added the EFL had signed a "memorandum of understanding" with its betting company sponsor which covers "best practice, protecting minors and the vulnerable".
A spokesman for the Scottish Professional Football League said the organisation was "aware of our social responsibilities" around gambling.
5 live Investigates is on BBC Radio 5 live, 9 September at 11:00 GMT - catch up on BBC iPlayer Radio.
Have you got something you want investigating? We want to hear from you. Email us.