Not necessarily. It puts it where it belongs: on parents. Parents who buy computers and phones for their kids have the responsibility of supervising their use. My own preference is that this would be something that parents are encouraged to use through public education campaigns.

But yes, depending of the level of strictness, it could also be enforced at point of sale. A fairly standard practice. We're already used to it with alcohol, cigarettes, knives. Heck, it's already done when buying a SIM for your phone. It has the advantage of preserving the most important part of privacy—the link between the person and their activity. The phone store knows you bought a phone and that you're an adult, but they have no idea what sites or apps you're using.