Explain that faith is believing in something that you cannot see. State that although you cannot see God (or Jesus) because He is a Spirit, you can still know that He is real. Explain that something else you cannot see, but is real is the air. State that you are now going to prove that the air in the room is real.
Pour water into a glass until it is almost full. Place a piece of cardboard, cut to slightly larger than the top of the glass, shiny side down, over the top. (An old breakfast cereal box is an ideal source of suitable cardboard). Hold cardboard in place, and invert glass. Take away your hand from the cardboard. Explain that gravity is still at work trying to make the water fall on the floor, but that the air – which we cannot see – is stronger than gravity and is keeping the cardboard in place.
Invite a few of the children to put their faith in the air – which they cannot see- and walk under the glass. As they are doing so, reinforce the truth that they are trusting in something that they cannot see.
If you wish, you could conclude this illustration as follows.
State that you are now looking for someone with GREAT faith. Choose a volunteer. State that you are now going to hold the glass of water over their head as before and tip it upside down, but this time you are not going to use any cardboard! Say you wouldn’t want them to get too wet if things went wrong, so you will pour some of the water out of the glass. Pour out water until about 2 or 3 cm. remains. State that you still don’t like the idea of wetting their hair – if things did go wrong – so you will hold a cup between the glass and their hair. Pour the water out of the glass and into the cup. Act surprised that the water came out of the glass. State that you have worked out the problem. You weren’t really using faith, because real faith in Jesus is trusting in Him alone. Therefore, real faith in the air is trusting in the air alone. Therefore you are now going to invert the cup (now containing the water ) over the volunteer’s head, but with nothing in between. Do this. The water will not come out of the cup, because you had previously placed a SPONGE in the bottom!
by Maurice Sweetsur, http://objectlessons.blogspot.com/