Thanks for the replies.
Well I put a few feelers out - it seems it has been mentioned before and they are aware of sources of help to do it etc, but they don't seem keen atm - they have other priorities this year apparently. So that might have to wait a bit. I've just discovered that my son's teacher runs an environmental club, so will be offering to help out in class soon, to see if she's more willing!!!
But I am more involved with our pre-school, so will start off with them maybe, though everything will have to be grown in pots as we've just had the playarea resurfaced.