Parents can't easily prevent their kids from going to those kinds of stores once they're at the age where the parent doesn't need to keep an eye on them all the time and they can travel about on their own.

The difference though is that parents are generally the ones to give their kids their phones and devices. These devices could send headers to websites saying "I'm a kid" -- but this system doesn't exist, and parents apparently don't use existing parental controls properly or at all.