Thanks everyone, for the comments on this. Bottom line seems to be that it will most likely work, maybe not plug and play, but with a bit of tweaking, so maybe the thing to do is buy one and make quite sure, before committing to a bunch.
They are getting quite reasonably priced now - ebuyer has the Ilyama 19 inch one for under 400, which is just about affordable.
Thanks for the comments about kiosks also. The security issues are not too bothersome. We will not allow outside net access at all, we'll put these machines on a separate subnet, and if there is no keyboard and it boots from read only media....?
Well, famous last words! Never underestimate the ingenuity of a bored 12 year old.
Peter