Is YouTube safe for children?
Short answer: not by itself. YouTube is not a children's site with some adult corners — it is a site for everybody that also has children's things on it. Whether it turns out safe depends on how a child arrives and what happens when a video ends.
What actually goes wrong
The problem is rarely the video you chose. It is the third one after it. The recommendations beside and after a clip are picked for what keeps people watching, which is not the same as what is suitable. A child who taps another thumbnail three times ends up somewhere nobody sent them.
There is also video made to look like children's programming and not be it — recognisable characters in scenes that do not belong to them. YouTube removes that when it is reported, and it keeps coming back, and a four-year-old cannot tell the difference.
What YouTube Kids does and does not fix
YouTube Kids is a genuine improvement: there is an age filter, search can be turned off, and you can build a list of nothing but videos you approved yourself. That last setting is the safest thing YouTube offers.
What it does not remove: the selection is automated underneath, so there is no person in the loop unless you tick every video yourself. And it is still an app choosing the next video by what performs.
What we do differently
Every video on KidsTube was watched by a person before it went on — that is the whole design, and it is also why we have a couple of thousand videos and not a couple of million. There are no comments underneath, and no recommendation sidebar offering something else. When a video ends, the next episode of the same show follows — not something an algorithm went and found.
In practice: a child who starts on Miffy ends on Miffy. That is the difference this site is built around.
What we do not solve
We are not parental-control software, and saying so beats letting you find out. There is no screen-time limit, no bedtime, no PIN in front of the grown-up parts, and no child profile — Recently watched belongs to the account, so two children on one tablet share a list. A limit is the first thing on the list of what is still missing, and the post on playing on by itself covers what that means today.
What is here is set out in full on How it works, including what an account keeps.