I would think you just need to explain what your role in the procedures are so for example in a fire your role would be to blow th whistle or sound the alarm or gather the children in your care and follow the procedures to get them out of the building to the designated fire area making sure no one is left in the building and then help with the roll call say whose role it is to phone the fire brigade and inform parents.
Do the same for the others as if it was really happening
