YouTube is absolutely amazing for kids if it’s curated properly (admittedly perhaps not that easy). There’s a huge amount of content like this that is aimed at adults, but can be roughly understood by a 5-6 year old.
It seems it might be related to legislation surrounding account ownership by minors, but I have no idea how to confirm it, esp since it's supposed to work when a parent controls the account.
The app is available as a standalone APK now: https://channelwhitelist-tilda-ws.translate.goog/?_x_tr_sl=a...
Unfortunately i could not find sources, but it works rather well and has English UI as well
Of course, parents have been asking for this instead of the shitty "YouTube kids" garbage for... ever? Basically? So clearly Google just doesn't want to do it, for whatever reason. Probably doesn't let them extract as much money from advertising to kids, somehow.