Ask HN: The best Internet browser for young children?

I'd like to start letting my oldest browse the internet. However I don't want to have to setup and find all the content for him.

I'm pretty sure I have seen startups come and go that look like they do this, but that was before the kids were old enough for me to remember!

Any recommendations? 5+ is the age range, but anything for younger is fine too.

Linux preferable (Raspberry PI etc), if not then a Mac, and if I must Windows.

Ta muchly!