I had to get pregnant to get an adequate ventilation hood on my kiln! (Hope you all won't have to go that far!) Sometimes I find it informative to talk to people who work for Ceramics supply places, i.e. Highwater Pottery in N.C.
They have a new hood that attaches to the bottom of the kiln and ventilates from there. I think it's called an "Enviro-vent" or something like that.
If all else fails, get the parents involved. None of them want their children exposed to harmful chemicals.