
Facebook's terms of service contain a provision that gives FB the right to utilize users’ name and likeness in ads. So, when people continue using FB after clicking acceptance, the terms of use become a legally binding contract.
The class of minors, however, insisted that a contract formed minors can be voided because of their age under California Family Code § 6710.

Minor plaintiffs intended to disaffirm (void) their contract by filing a lawsuit. But in order to disaffirm a contract, one would have to reject the whole contract, not just the provisions they don’t like. Ninth Circuit cited a 1935 case, Babu v. Petersen, where it states that the general rule of California law is that “a party cannot apply to his own use that part of the transaction which may bring to him a benefit, and repudiate the other, which may not be to his interest to fulfill.” Minors continued using FB after filing their lawsuit. So, the Ninth Circuit determined that “[b]y continuing to use facebook.com after bringing their action, Plaintiffs manifested an intention not to disaffirm the contract.”