For your computer: https://help.ubuntu.com/stable/ubuntu-help/parental-controls.html.en

For the Phone I'd create a second profile on the phone and only install the apps there which I'd allow my children to use.

There are parental controls, but it's rare. FOSS projects usually aren't very keen on building systems of authority, even parental ones.

For smartphones check out /e/OS (Murena Smartphones). They added parental controls recently, not sure how good those are though.

For computers your best bet's probably a Linux with Gnome. They also added something recently.

You might be able to combine both with a custom DNS service, surely there's something out there for that usecase (NextDNS?). But that's already getting pretty complex.

Overkill, otherwise there’s parental controls built-in to iOS/Android

https://github.com/fleetdm/fleet

It's called MDM. Unfortunately most companies try to limit their MDM solutions to enterprises, but FleetDM is an okay choice.

depending on your router, couldn't you do this at that level? a combination of public dns (dns4eu) or adguard filter lists? you could create two wifi networks, one controlled one not; most routers let you block whole services too like tiktok, etc

What is it?

What is family link? Active directory control for Android?

No, not really.

I have a whole complex setup including unique profiles and auth with unique limitations per user on services, like what books are available on the eBook server, what shows/movies they can see, even which block list is applied for DNS.

But things like app restrictions on a tablet are entirely manual. I kiosked off and will manually install via adb.

There isnt really an equivalent single tool I'm aware of.

what type of phone/OS are your phone and computer?

there's some hands-on controls too that may be useful but it starts with just giving them their own profile or login that's ideally with as few permissions as possible. For android, there's profiles which you may be able to lock down a bit more than your own profile. Apple had family mode settings that you may be able to turn on and off when they have the device. For a computer, same approach. Standard user account with whatever you installed using an admin account and lock down content via DNS like cloudflare for families, https://adguard-dns.io/public-dns.html, a self hosted one or something like https://nextdns.io/.

Android has app-pinning, iOS has guided access. They are functionally the same thing, in that they lock the phone to a single app. Basically a sort of kiosk mode.

Barring that, if you really want some form of parental controls for the kids, I would recommend just getting a phone from the likes of Pinwheel, Gabb, Bark, etc. They are purpose-built for kids.

For PC, at least on Linux, there is an application called timekpr-next that handles screentime. It's pretty handy.

Not a perfect solution, but I use NextDNS which has profiles, and can set allowed services and times of day for them, Online Games, Video Streaming etc. This is set in the phone's DNS setting so works via WiFi or cellular.

I've started to use the excellent DNS Toggle on my phone to quickly enable/disable it for the really annoying sites that block ad blockers etc.

In terms of app control itself, I still use Family Link begrudgingly as well like you for Android phones. I access it via the web page which thankfully still works so I don't have to have the Google app installed.

For straight up app control, timelimit does a far bit of what your asking.

Nothing really exists.

The likely extreme thing I did was setup ManageEngine's MDM+ (free for<25 users) and put my sons phone on a "device profile" which locks it down. It's decently intuitive, but does require a "server" so there's a bit of setup too. I use YT at work too so for me it was done in 30 minutes.

OMG you gotta look at this:

And

Nah, man. The answer is kids don't need to be on the internet. They need to not be on the internet or on a data plan until they go to college and they gotta pay for that service.