A watchdog has urged social media giant Facebook to stop letting advertisers target 'pre-teens'.

The Consumers Union, The Center for Science in the Public Interest and Children Now are said to have sent a letter to Facebook CEO Mark Zuckerberg urging that children have a “difficult time differentiating between advertising and other media content, especially in the digital context.” The letter further states that any “Likes” that children proclaim “not then be used to target that child with ads, nor should it be used to conduct social media marketing, in order to convince the child’s friends to also interact with the product or company.”

The news comes just as Facebook is reportedly considering opening up the site to kids under 13.

In an email to the The New York Times, a Facebook rep said:

“Enforcing age restrictions on the Internet is a difficult issue, especially when many reports have shown parents want their children to access online content and services. We welcome today’s recommendations by consumer, privacy, health and child groups as we continue our dialogue with stakeholders, regulators and other policy makers about how best to help parents keep their kids safe in an evolving online environment.”

In 2011, a Consumer Reports survey found 7.5 million Facebook users were under 13.