Plants for a wildlife garden?

The RHS has a gardening with schools info page, it might help you. Also, articles with gardening for wildlife in mind. As for a tree, British natives have the most value to wildlife, the oak being the most obvious, but I see you want a small tree. A Rowan maybe, Sorbus 'Joseph Rock' flowers and berries or Sorbus aucuparia. Bulbs could start with snowdrops, through crocus, to early dwarf narcissi, camassia looks good growing in grass likes a dampish not wet soil, alliums grow well in shade and are good for many insects. Also umbellifers on the woodland edge. THis is a huge question! Will let someone else have a go. Good luck, sounds like a lovely project. Oh and don't forget a wood pile for mini beasts. Lou x

Make plans with the children, not to plant them but their ideas will give them a long interest in the project.
To start at the bottom of your question I would say an oak is a good tree, which is very slow growing and can be looked upon by the children in later years.
I can send you some Helibores and other seedlings which are wild flowers in their own right. Bluebells, Campians, Primroses, Marsh Marigold, Daisies/Margueritas and Bog grass are just a few ideas. Sedums in a dry spot need little or no attention. Good luck with what you are doing.

Doctorbob1 you sound like a star! :) I have tried developing planting plans with the children and they have given some of their favourites which we intend to include. Its getting it right that worries me! The children at the local secondary school have raised most of the money and are doing the hard work, our children are hopefully going to be doing the planting. So its important that I spend the money well and plant everything for the greatest amount of success.

Lou, thanks for great ideas.
Dimapps

As you say Dimapps, a tall order, but one with which I'm sure you'll have great success. As you have a partially shaded area, can I suggest one of my favourites...ferns. They are quite diverse in their leaf forms, and the children could enjoy watching the new fronds, like shepherds' crooks, gradually unfurling. All the best with your project.

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Do you have any public gardens near you? These days, it's quite possible that they may have an outreach programme offering help with getting schoolchildren involved with plants of all forms.