I’ve been working on setting up laptops for my kids and Microsoft has done a ton on this. Create them Microsoft accounts and log tbem into their windows machine with said account. You can then manage that device from your Microsoft account. Block apps, setting screen time, web filtering using Edge, your kids can request access to apps and you can approve it from an app, and you get reports every week of their device usage if you want. Overall I’m honestly surprised how much control it gave me.

At the end of the day having multiple layers is the best approach. Setting up both a DNS filter like pihole and using managed accounts should stop most unwanted usage of devices.

I’m throwing a vote in for Folding@home. Great way to help science, and you can run as many instances as you want to really put pressure on your server