Linux systems are used all over for enterprise use cases, which means there is a robust user permission system. Usage won’t be Googleable with stuff like “parental control” but more likely keywords like “user restriction”.
Not sure if you mention your wife because she knows Linux and thinks it’s a bad idea, or because doesn’t know Linux, and still thinks it’s a bad idea.
Of course, when your kid one day learns to flash an iso onto a usb, and install an OS, any and all parental control will be symbolic. Hopefully you’ve successfully taught your kid how to use tech safely by then.
You’ll want to look into browser extensions and blocking websites on your router, as well.