Gambling websites have been told to remove any "unacceptable" advertisements that might appeal to children right away.
Operators have received a joint letter from regulators encouraging them to advertise appropriately and threatening punishment if they don't.
The article mentioned games with titles like Fluffy Favourites and Pirate Princess that featured cartoon characters in vibrant colours as examples that can tempt kids to gamble.
The Gambling Commission, the Advertising Standards Authority, the Committee of Advertising Practise (CAP), and the Remote Gambling Association addressed the letter to more than 450 businesses.
The regulators emphasised that vulnerable individuals under the age of 18 should be shielded from exploitation.
The letter said: "We are writing to advise you to amend or remove immediately any ads on your website or in third party media that are likely to appeal particularly to people aged 17 or younger… and generally available to view.
“This relates particularly to freely accessible ads for play-for-free and play-for-money games and includes all graphics and images displayed on a website or in third party media.
The use of certain colours, cartoon and comic book imagery, animals, references to children and youth, and game names like Piggy Payout, Fluffy Favourites, Pirate Princess, and Jack and the Beanstalk are likely to increase attraction to those under the age of 18 either individually or in combination.
The statement said, "You must immediately amend or remove any freely accessible ads on your website or in third-party media space that are likely to appeal particularly to under-18s."
The letter included a warning that failure to abide by the CAP code, which mandates socially responsible marketing communications for gambling companies, could result in penalties.
According to statistics conducted by the Gambling Commission last year, around 450,000 kids bet weekly. Of those, 9,000 were deemed to be "problem gamblers".
The Local Government Association (LGA), citing councils' prior requests for tighter limits, supported the action.
The LGA's Safer and Stronger Communities Board chairman, Councillor Simon Blackburn, said:"Problem gambling is a major concern for councils which can cause greater personal harm.
It can lead to spiralling debt, deteriorating mental health and wellbeing, and a toll on society - and taxpayers - through crime and disorder, family breakdown and homelessness. It is vital our children and young people are kept safe and protected from the problems gambling can cause."
New Customer Offer, T&C Apply. 18+
18+. Terms apply. Please gamble responsibly.
