How to limit icloud storage for kids?

not really sure how it is not possible to limit storage when family sharing. A guardian should be able to limit the kids’ storage. Bit ridiculous since the guardian could control a lot of other things except the storage. Maybe there should be a set model like limit 10-50GB per user when having less than 2 TB and maybe 100-200GB per user when having 2TB. This shouldn’t be hard to develop and probably be useful for family users as well as apple in the long run.