Materials

a large clear plastic bottle with cap 
a measuring cup 
cold and hot water 
matches (Handled by a grown-up)

Procedure

Pour 1/3 cup of cold tap water into the clear plastic bottle and put the cap tightly back on. Then shake the bottle for 30 seconds and set it on a table. Squeeze the bottle and then release it. Repeat this process several times. 

Do you notice anything different about the bottle? Inside the bottle? 

With an adult helping you, remove the cap from the bottle. Hold a match over the bottle's mouth. Now, blow out the match by quickly squeezing the bottle. Then slowly release the pressure on the bottle to draw the smoke into it. Replace and tighten the cap on the bottle. Then squeeze and release it several times. 

Do you see anything different about the bottle now? Did a cloud form in the bottle? Why would a cloud form now that you've added smoke? 

Clean out the bottle well and pour 1/3 cup of hot tap water into it. Then repeat Step #2 again, using hot water. 

What happened differently this time? Was there a bigger cloud than before? Why do you think it was bigger?  .