Given how broadly the commerce clause has been interpreted I don't think we can rely on that to save us here. Criminalizing Bob publishing his OS on GitHub is still too authoritarian for my liking.
Just off the top of my head, something like "physical hardware with web access sold in the US without an ID check at the checkout counter must include this feature in its preinstalled OS" would be a better way to write the law in my opinion. Plenty of ways around it if you're a hobbyist or for some reason really don't want to comply, but a big enough hassle that all the major commercial OS providers would probably find it easiest to just include the feature. (Especially since this is a feature most parents would probably appreciate anyway.)
Just off the top of my head, something like "physical hardware with web access sold in the US without an ID check at the checkout counter must include this feature in its preinstalled OS" would be a better way to write the law in my opinion. Plenty of ways around it if you're a hobbyist or for some reason really don't want to comply, but a big enough hassle that all the major commercial OS providers would probably find it easiest to just include the feature. (Especially since this is a feature most parents would probably appreciate anyway.)