Enforcement for the new rules should take effect in the "coming weeks," Facebook said. It's also working on tools to help creators honor the new policy, such as setting minimum age requirements or their content.

This is the first time Instagram is limiting what influencers can pitch in their feeds, and it's considered overdue by some. Facebook and Instagram have both come under fire for letting social media stars advertise harmful products, including possible underage users. In some cases, those stars don't understand the products or even use them. And to some extent, Facebook might not have much choice. The UK's Advertising Standards Authority, for instance, banned Instagram posts that appeared to show under-25s promoting vaping. If the company doesn't ban these posts itself, it risks further heat from regulators that might impose their own restrictions.