The purpose of this activity is to help your child compare different containers and how much liquid they hold (capacity), guess (estimate) and then measure to find out. These are important steps toward understanding measurement.
Safety note: Children should never be left unsupervised around water.
This activity can be done during bath time, at the sink, or with a plastic tub filled with water. Let your child explore filling up the three different containers. “How many small cups of water will it take to fill the biggest container? Let's count!” Help your child arrange the containers from smallest to largest. “Which holds the most water? The least? Which is the heaviest? The lightest?” “Try pouring the large container of water into the smaller one. What happens? Why?” (It overflows because the small container can't hold as much water as the larger one.)
Next time the forecast calls for rain, set out a large plastic container on a level surface outside to collect the rain. When the rain is over, bring the container inside and estimate how much rain water is in there. Is it enough to fill the smallest container? The medium-size? You can do the same experiment when it snows.