As much as I love Google (not even a little, my love for that company is negative and becoming more negative per second) I would love to run far far away from it. Here's another ball and chain I need to break.
Where can I find a simple parental control access system for my phone and or computer that I allow my kids to use?
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.