The countless brands trying to figure out how to take advantage of Facebook and produce an ROI received some good news, and bad news, today.

The good news: the world’s largest social network is reportedly looking at ways to open itself up to preteens. The bad news: the world’s largest social network is reportedly looking at ways to open itself up to preteens.

According to the Wall Street Journal, Facebook is exploring a number of mechanisms to make Facebook use by those under the age of 13 legally viable. These “include connecting children’s accounts to their parents’ and controls that would allow parents to decide whom their kids can ‘friend’ and what applications they can use.” There may even be plans to enable parent-supervised payments.

It’s not hard to understand why Facebook would want to open its site up to under-13s. There are an estimated 7.5m children in the United States who are using the popular social network in violation of the company’s age restriction, and with this in mind, child safety groups and politicians have been pressing Facebook to find a way to deal protect children.

The most obvious way, of course, is to allow preteens onto the social network, which would, incidentally, be a boon for the social network.

After all, with more than 900m global users, the number of large markets Facebook has yet to tap can be counted on one hand. The ability to open its doors to preteens would give it a sizable new demographic group to court, particularly in the lucrative developed nations where Facebook’s growth has slowed the most.

That, in turn, would create new opportunities for Facebook to deliver a potentially lucrative preteen audience to brands eager to market to kids before their brand preferences are established. Indeed, the Wall Street Journal reports that Facebook has already held discussions with companies like Disney about the possibilities.

But brands should tread carefully here. While being able to engage with under-13s on Facebook might be an appealing marketing proposition, it isn’t without its challenges. That’s because even if Facebook implements technologies that enable it to comply with the laws around children s’ use of online services, brands active on Facebook will still need to grapple with thorny issues.

Would brands need to create separate experiences for preteens on Facebook? Would special training and new policies be required to ensure that community managers and customer support staff handle interactions with under-13s appropriately? What sort of moral boundaries would need to be established relating to ads targeted at children? Is it worth targeting them at all?

These are but a few of the questions brands would face if Facebook officially opens up its doors to preteens. The answers probably won’t be immediately obvious for many brands, and at the end of the day, brands already grappling with making social media marketing work may be left wondering if “it’s complicated” is more than just a Facebook relationship status.

Indeed, “it’s complicated” may prove to be the best description of marketing on Facebook period.