1. What is the age range of children? 1.1 Definition of child A child refers to a person under the age of 18. This definition is also adopted by UNICEF. In, children\’s age range is 0-14 years. 1.2 Child development stages Child development stages can be divided into the following stages: neonatal period, early childhood, preschool period, adolescence and adulthood. Each stage has its own unique characteristics and issues that require attention. 1.3 Children’s psychological development Children’s psychological development refers to the process of gradual change and improvement of human psychological state from birth to adulthood.