Build kid friendly apps. i.e Primal Kids and only let them use that app, locking down their devices.
Discussion
I'm not sure that there are such things as kid friendly apps. My personal approach is no smart phones of any sort until 16. Minimum.
Respectfully, that doesn’t work. My kid was 16 in 2008 and had somehow added 5,000 “friends” to her Facebook. I took the phone and charger away, and it’s a life lesson. It can’t be all or nothing. We have to parent them and teach the life lessons. And we have to empower them to learn WHY the behavior is wrong and WHY we take the phone away until they can understand the many dangers of social media.
I don't understand why it doesn't work. It's working so far and they're not that far off 16.
Would you give a child a gun until they shoot someone and only then take it away to teach them why that behaviour is wring? Or would you prohibit gun use until they're old enough to use one responsibly?
Social media is _incredibly_ damaging to children's developing brains. My kids and their friends who have "brickphones" are avid readers, can hold conversations and have long attention spans. Their friends who are smartphone addicts are way behind where they should be in terms of reading ability, can't concentrate on tasks and are in some cases showing signs of mental health issues already.
There is awareness of the impact of social media on children's developmental health, but it's waaaaay behind where it needs to be.
If you haven't already, read this

Sounds like you have them in a bubble?
Nope. I wasn't in a bubble when I grew up without smart phones. Were you?
🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣 I am Gen X dude! We didn’t have them when I grew up!!!! 💀💀💀💀💀💀💀💀💀💀💀
That's exactly my point. Dude.
How do your kids and their friends all have brick phones? That’s a bubble.
What? You're making very little sense. If that's your position, everyone with a smartphone is also in a bubble. In fact, given that viewpoint, everyone on earth is in a bubble.
I guess you don’t get what I’m saying. Your kids have brick phones and so do their friends. How is that possible? I haven’t seen one kid with a brick phone, let alone several. What world is this where kids have zero smart phones and their friends are the same? Sounds fascinating.
https://www.smartphonefreechildhood.org/
This is gaining traction in the UK.
Smartphones are banned in a lot of secondary schools here.