OS makers should not be in the business of enforcing censorship. If you want to shield your children from the "horrors" of the internet either use proper parental control software, or don't allow access at all like you said until your kids are mature to understand what's going on
The onus is on the parent to the be parent. Not the tech industry, and especially not the government.
Who are you to decide what should or should not be?
"proper parental control software" doesn't exist for a lot of the platforms.
If the solution is parental control software, that also puts onus on operating systems to present the means for such software to work properly. This does not mean the OS should censor, it might mean the OS offers a censorship interface.
At least we seem to agree the solution lies with better tools for parents.