The banner ad for Ewank.com, which appeared within the app ‘Talking Tom’, displayed large text which read "EWANK" , alongside an image of three naked women engaged in sexual activities with four other women.
A parent, whose five-year-old child had been playing the game when the ad was seen, complained to the Advertising Standards Authority that the work had been "inappropriately and irresponsibly placed".
Mobjizz Ltd, on behalf of Ewank.com, said it allowed its website to be advertised by third parties on affiliate ad networks under agreements with strict clauses.
But, it added, the appearance of the ad in the Talking Tom app was a clear breach of its affiliate contract and it was keen to take action against the affiliate involved, but was unable to identify it.
Outfit7, the operator of the Talking Tom app, said it had a strict advertising policy on age-appropriate ads, but had not been able to identify which ad network had served the ad.
In its ruling, published today, the ASA said: "The sexually explicit content of the ad and the product it promoted meant it should not appear in media which might be seen by children.
"In this case the ad had appeared in an app which would be of particular appeal to children."
The ASA ruled that the ad should not appear in media which might be seen by children, including the Talking Tom app.