My primary school had a completely concrete playground without any kind of plants at all.
Nowadays (yes, it's a lot of years later) they have made one big corner of it into a nature garden, added a couple of trees, and the concrete area has since widen planters with greenery and flowers in them.
So there is progress, but it should absolutely be a standard for kids to be around plants as much as possible and for no schools to have completely concrete yards.