You need to put cold water into a bottle, then empty it out again.
Light a match and drop it into the bottle.
Squeeze the bottle.
When you stop squeezing the bottle, hey presto, you have a cloud in the bottle.
How does this work?
Clouds are formed when water droplets in the air cool and then collect on dust particles. In this demonstration, the dust particles were provided by the smoke from the match. The air inside the bottle was cooled by releasing the pressure after the bottle was squeezed.
We were delighted to be able to make our own clouds!