M.M.
Personally I wouldn't use skewers in a class of 18 kids, no matter how old.
You can do apples and caramel dip
Celery and peanut butter, if pb is allowed, with raisins
carrots and dip
grapes
And bring cookies, a Christmas party is no fun without cookies, is she bringing them?
Added: PB&J has a good idea using toothpicks. I just envision 9 boys running around with skewer swords. Maybe because that's what mine would do.