First question would have to be - how much do the kids respect the plantings? If they sit on, walk over, drop rubbish in, then you'll need to plant something different from that which you'd plant if care was taken.

I'd be a bit wary about the rosemary and such. Bees are attracted to these plants - and some kids are highly allergic to stings.

What's locally native for you? If you have any natural science work as part of the Science curriculum then the planting could be a useful resource as well as an attractive feature.

Otherwise - perennial coloured grasses and, perhaps, Echeveria species or varieties?

I had great success neglecting plants like cosmos (several varieties, and you should deadhead to keep the blooms coming, but that goes for lantana too), russian sage, coreopsis (also lots of varieties - I like tickseed as well as moonbeam); and the wonderful biennial lychnis coronaria, a.k.a. rose campion. They were all tough plants in my garden, and the non-perennials were good self-seeders.