Legally there is none. Both are considered minors, not capable of giving informed consent for (in many US states) marriage, employment, military service, voting

Legally there is none. Both are considered minors, not capable of giving informed consent for (in many US states) marriage, employment, military service, voting, driving, or opening a bank account independently. And it's not like Facebook deserves rebuke for exploiting 5-year-olds and a Nobel Prize for exploiting 15-year-olds. But it's also true that the content of the article doesn't support the headline. Edit: Even the math is wrong. If they're asserting that everyone's eligible to be called a "whale" who plays Angry Birds, and that the average age of an Angry Birds player is 5, then the minimum age ("as young as") of a whale isn't 5, it's less than 5.