Apps featuring sexual or violent content have been approved by Apple and Google as suitable for young children.
An investigation by The Times revealed details of multiple games featuring adult themes aimed at 12-year-olds, with some even rated as low as "4+".
One reporter signed up for an 'anonymous chat' app certified as suitable from age 12, where he was accosted by other members with profile pictures of topless teenage boys asking him for nude photos.
Apple and Google both allow developers to decide on a rating for their games, with the tech giants then verifying the certifications are suitable.
Some of the available apps include: "Boyfriend craft," where players can become a "lover" in the office and seduce their best friend, and another game that forces users to choose whether to have sex with a woman or "insult her."
The Department for Digital, Culture, Media and Sport said: "We expect robust processes to prevent inappropriate content being accessed by children in app stores.
"The industry needs to step up and make these platforms safer, and if progress is slow, we do not rule out regulation."
Tony Stower, Head of Child Safety Online at the NSPCC, also criticized the ratings.
He said it is "absolutely clear" that apps with sexual themes are "completely inappropriate for children and could even be harmful".
He added: "Google and Apple must ensure app descriptions and age ratings accurately reflect the risks of using each app, as this enables parents to understand if they're appropriate."
A spokesman for Google said if apps breached its policies, they would be removed, while Apple has already removed most of the games highlighted by The Times.
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