The ads for LottoGo EuroMillions, William Hill Vegas, Betfair Bingo and Dunder came up in the Looney Tunes World of Mayhem app in February.

All four firms say they have since stopped working with affiliate company Tapjoy, which placed ads on the app.

The ASA ruled the ads must not be used again without limiting the risk of children being exposed to them.

In its ruling, the Advertising Standards Authority (ASA) said Tapjoy acknowledged the Looney Tunes app had been mistakenly categorised with a "mature-gambling" setting.

And Scopely, the publisher of Looney Tunes World of Mayhem, told the ASA it did not target its games to children, and noted that individuals under the age of 16 in the EU are not permitted to play the games.

The game has a rating of PEGI 7 in the UK Google Play app store, meaning it was suitable for players aged seven and above.

It allowed users to build worlds and situations based on the Looney Tunes cartoons and collect characters to "battle" each other.

The ASA said: "Given the use of cartoon characters, cartoonish violence and the relatively simple nature of the game, we considered it was likely to appeal to many under-18s.

"However, we acknowledged that the characters would be well known to older players, and the game was likely to have more general appeal."

William Hill told the ASA it is conducting a full review into work with its affiliates to prevent the issue happening again.