FACEBOOK let kids rack up huge bills on its games despite suspecting they were under a 13 age limit, court files show.

Mark Zuckerberg’s social network also knew its average Angry Birds player was aged just five.

The network refused to void a £5,000 bill which one boy ran up on his parents’ card for purchases on another game.

Two staff debating if the lad was under 13 callously labelled him a “whale”, the term for casino big spenders.

The files, from a 2012 lawsuit, were revealed to the US’s Centre for Investigative Reporting.

Parents expecting safeguards to kick in to stop purchases were refused refunds. This led one worker to say Facebook had created a “Frankenstein beast” of a system.

Some staff voiced concerns but they appear to have been ignored.

Facebook was unavailable for comment.