Easy way to limit internet usage? Leap 42.2

Good day all, I would like to know how to set a limit of so many gigs/30 days limit of internet usage for each kid, is this feasible? I can easily set a user account for each but just no idea how i can set a limit. I know my router can be set to shut off internet on a schedule but this is not what i’m looking for, thank you.

As your post suggested, there is a general software category called “Parental Controls.”
Google that for software you can either install or configure your machine to proxy through.