When my older son was about 15 months old, we wanted to safely expose him to different substances and sounds. We purchased 4 jars of the same size at a discount store. We put sand in one, rice in another, then used black-eyed peas. For the last one, we put a few ounces of water colored with food color, then put a few ounces of cooking oil with it. It is important that you fill the jars no more than 1/3 full, so the substances can be shook. Be sure to superglue the lids (or seal with a glue gun), then let them dry overnight just to be sure of the seal. Imagine the expression of your toddler as he hears the difference between the sound of the sand and the sound of the rice. And we all had fun with the oil and water, shaking it to make it combine, then setting it down for awhile and coming back to see the substances separated. Later, my son expressed an interest in my thick dishwashing liquid. So we created another jar with that in it and watched him become facinated as the stuff traveled slowly in it. Have fun making your own jars!