Sorting. It is an activity that everyone does everyday. Think about your life: Some people sort clothes by color, groceries by kind, toys by function, shoes by season, paper by size, ect. So as you can see from your own life, sorting is critical in early development for children. 
Sorting is a beginning math skill. 

By sorting, children understand that items and ideas can be similar or different as well as be organized into certain categories. By practicing sorting so young a child will benefit later on by being able to group numbers and sets.   Studies have shown that kids who are used to comparing and contrasting do better in mathematics later on and ultimately in organizing their own lives.