The social networking site has filed a patent with US Federal Trade Commission that would make it possible for children under 13 to set up an account as long as they have approval from their parents.

So, if an underage user tries to access the site, Facebook would ask for "parental authorisation" via an existing account.

The child would tell Facebook who its parents are before the site runs a validity check on the parent's account to confirm the relationship, and the age of the user, Facebook said in the patent.

"Upon successful verification, the online service allows the identified user to authorise account creation for the child user, and/or manage the account and actions of the child user," Facebook officials said.

Once an underage account had been linked to a parental one, the adults would be able to limit and monitor their child's behaviour.

They would also have complete control of the child's privacy and applications on the site.

Facebook was criticised last year for letting teenagers make their posts public.

(Agencies)