Pennington Infants needs your advice!

The sensory garden at Pennington Infants' School is up and running! The gnarly, old oak tree now has sturdy decking around it and the raised flower beds wait  in anticipation for planting. The paths are ready for the trample of excited little feet and the insect boxes await many-legged friends.But we may have a problem - how do we entice them without the flora? Please can you give us advice on how to fill our garden with wonderful plants on a very small budget?