Do you have a contact with anyone at the council who can lend you a hand wash test kit?
You paint hand with an invisible dye, go an activity for a while and then get people to wash their hands. You then pass them under the light (I think it is UV) and it shows all the areas that they missed when washing.
Show how important it is to wash hands properly. stand everyone in a line. Take your right hand and dip it in red paint. Shake hands with the first Cub. who then turns and shakes hands with the next, and so on. By the time the handshake gets to the end of the line your red bugs will have contaminated everyone.