Q: My son can count, but has problems determining “how many” are in a set?

Understanding “how many” are in a set — known as the “cardinal principle”, is a difficult concept for many young children to grasp. Most children begin to understand this concept around 4 years of age, but it can take up to a year to master. You can help your son learn the cardinal principle through your everyday activities. For example, counting the number of apples you buy at the grocery store, counting the number of toy cars your son has, counting while playing hide and seek, and labeling familiar items in sets (“you have five crayons”). The more exposure to “number talk” a child has (particularly that involve number sets greater than 4), the more likely they are to understand and master the cardinal principle.