Give the child three containers of different sizes. Ask “If we want to find out how much each container can hold, which of these three cups would we use to measure the capacity of all three containers?” (Guide the child to discover they would need to use the smaller container as the “base” to measure the capacity of all three). Record the capacity of each container along with a picture of each.
Use different sized containers and allow the child more time to explore with 'big' and 'small' containers by trying to pour the bigger container into the smaller. This will further reinforce the concept of 'bigger' and 'smaller' capacity.