How do you limit data usage without doing it for individual apps.

I'd like to limit my child's Data usage to a certain amount.

On Samsung it's as simple as going to Settings > Data storage > and set your limit. it even shows you in a graph how much you've already consumed.

But when i did my search for how this could be done on iphone, there was no straightforward answer and it like needed to be done on a per app basis?

I'm not a techie person, so please bear with me...

How do i limit the data usage - in the same way I described above?

Thanks.