If you want that you get an OS that specifically supports child mode, you don't mandate all OSs default to having a child mode. The reason you don't do this is because when it's in place the default will be if you don't want to prove who you are you can't go anywhere on the internet except the most milquetoast sites (with no user created content) and the worst of the worst sites (that ignore these rules).

If I want to bash the government I don't want to have to choose between giving my id and going to terroristforum dot com.

If you're trusting a 5-year-old with a computer (connected to the internet, no less) and then letting them use it unsupervised, then you would already be putting a lot of trust in sites implementing age controls correctly (or at all). And if there's anything we know about the Internet, it's that web sites can be trusted, right? :-D Keep in mind, whatever law California passes, there will be web sites outside of Cali jurisdiction.

What's worse (and the point of the linked article), a kid who's not 5 but 10 would be very able to bypass this particular requirement, making it utterly useless. It's about as effective as the "parental controls" on Leisure Suit Larry. I'd argue that this is worse than nothing, because now the parent believes they have a working parental control mechanism when they actually don't. Which means you now have a 10 year old online without parental controls AND possibly without parental supervision.

What works:

- Talk to your children about what they can be finding online.

- Don't let children as young as 5 onto the internet unsupervised.

- Build trust with your child. Try to make sure your child trusts you enough to come to you if they encounter material they're not comfortable with.

- If you don't have that relation of trust, your child will hide their online "failures" from you. They are then more likely to be victimized by online predators by blackmail etc.