9. Talk to Your Child About Quantity Conservation
For a three- or four-year-old, the height of something means more than the volume of something. For example, if your child sees a tall, juice-filled cup and a shorter, wider cup that contains the same amount of juice, she may think that the taller cup has more liquid because of the cup's appearance. Show her how both cups actually hold the same amount of liquid. Kids start to understand conservation of quantity around age 5.