I helped at my daughters school. I avoided anything with thorns. but i used ones that would attract butterflies. Verbenna bonariensis, Scabious, asters [for the autumn]. We also grew nasturiums, calendula, 10 week stocks, nigella cornflowers, virginia stock. the children did these as part of the exercise.

As for little Tarquin nibbling as long as obviously poisonous plants arnt used [nightshade etc] there shouldnt be a problem. after all buttercups are posionous if you eat enough of them.

long wavy grass and bamboo. Nice textured paths and lots of spongy grass

I think some good questions to ask yourself are whether the garden area is going to be cared for on a regular basis and whether the kids are going to grow some of the plants themselves. If they're going to grow some plants, can I suggest Coleus. I grew a mixed pkt of Coleum when I was a kid and they're great - very easy and the amazing leaf patturns and colours are visible as soon as the seedlings get their first true leaves. Then of course there are some fun varieties of sunflowers. Cosmos is easy too. These are all annuals of course.

Many thanks for the answers thus far, but they are mainly annuals, so what about shrub choice, anything??

Well, I think anything that's not spiney.....'spose Tarquin might scoff berries, so avoid those...... What about Bracyglottis monroi, which has interesting velvetty silvery leaves with interesting wavy margins. Stacys (lambs ears) is a perennial with soil furry leaves too. Cistus purperea is a personal favourite which might be suitable - lots of big pink flowers that last a day - but it's not completely hardy (mine for the first time in 10+ years has got burnt this winter).

Well, I think anything that's not spiney.....'spose Tarquin might scoff berries, so avoid those...... What about Bracyglottis monroi, which has interesting velvetty silvery leaves with interesting wavy margins. Stacys (lambs ears) is a perennial with soil furry leaves too. Cistus purperea is a personal favourite which might be suitable - lots of big pink flowers that last a day - but it's not completely hardy (mine for the first time in 10+ years has got burnt this winter).

I would include texture and smell as well as the look! Perhaps flowers that could be picked, dried and pressed by the children? Bulbs are interesting too.

What about herbs....rosemary can be pretty bush-like,sage can get quite big and lavendar and obviously they are edible

The RSPB give excellent advice if you want a garden for wildlife. http://www.rspb.org.uk/advice/gardening/wildlife-friendly_garden.asp
A Rowan Tree would provide interest from the leaves appearing in spring, flowering, producing berries and being raided by the birds in the autumn. Buddleia now comes in a size to suit a patio pot and will attract butterflies. A garden that looks after itself does not stimulate children as much as growing their own veg in a raised bed would. It all depends on the size of the space availabe to you and whether the teachers want to use it as an educational resource and very important who will be responsible for caring for it over the holidays.

Many thanks for all the answers, i have a lot of info there and will take it all with me when i visit, once again, thank you..