This is how I started. I cut a piece of cardboard in the shape of a grape cluster and taped balloons to each side. I also taped a pole across the top so that it could be carried. Added greenery tissue paper and voila! Giant Grapes!
We left our 'camp' (classroom), climbed up the 'mountain' (stairway to the prayer room/stage area), spied out the high walled 'city' (Sanctuary), saw the 'giants' of the land (grownups), entered a 'garden' (my office) and found these grapes. We 'secretly' carried them back to the 'camp' and proceeded to 'share' each grape. Some of them 'popped'.
We need nourishment after all of the excitement, so we had real grapes, juice and goldfish to finish off the class. What a blast!
Oh and to begin with we made spyglasses out of cardboard rolls from Christmas wrapping. Simple but they loved it!