Kashmir Hill:
Four months after this study happened, in May 2012, Facebook made changes to its data use policy, and that’s when it introduced this line about how it might use your information: “For internal operations, including troubleshooting, data analysis, testing, research and service improvement.”
So not only did Facebook sneak in the “OK” later, but according to Hill there is no reason to believe that Facebook excluded people under 18 from the study.