In order to understand our children's behavior, it is important to be aware of where they are in their development. 

Children's levels of development differ based on personality, individual abilities, genetics, environment, etc. 
Next you find what is a general average of children's milestones by age.
 

My Child By Age

4
Years Old

3
Years Old

5
Years Old

Extracted from the CDC webpage: 
"Developmental Milestones" 
It contains information, examples and fun/comprehensive videos to watch.