A friend of mine found a bubble/fog machine (if you can find a great deal after Halloween, that sounds like tons of fun!) It blows bubbles that have fog in them. The solution lasts for 4 hours.
Kids down the street threw a Halloween party last year-they had apple bobbing, served eyeball punch (peeled grapes in red punch), gave party favors, had a best costume contest, had a strobe light & creepy music.
Since Halloween will just be over & they'll have tons of candy already, what about decorating apples? You supply the apples & decorations (caramel, chocolate shell, chopped nuts-check for allergies w/parents!, mini M&Ms, smashed candy bar pieces, sprinkles) & they supply creativity. Better than sending them home w/more candy! You could look around for a themed pinata (about $20 regularly) & fill it w/creepy goodies (squishy eyeballs, spider rings, Halloween fruit snacks if you can find them-but more goodies than food) & send them home w/a decorated paper bag w/their goodies inside.