COUNTING AND CARDINALITY. Preschool and Kindergarten math activities. Subitizing game with Dinosaur's eggs. Subitizing is one of the building blocks of number sense. It means being able to see a quantity of items, and instantly knowing how many. Recognizing quantities without having to count is a great foundation to building number sense. When students have number sense, they understand how numbers work, the relationships between them, and are able to use the numbers in real-world situations.