Here's why:
* No Global Registry: There is no central database or official count tracking the number of children worldwide.
* Changing Numbers: The number of children fluctuates constantly due to births and deaths.
* Definition of "Child": There is no universally agreed-upon definition of what constitutes a "child" (age range, etc.).
However, we can estimate:
* The United Nations estimates that approximately 2 billion people are under the age of 15.
* This number is constantly changing, and different organizations may have slightly different estimates.
It's important to note that these are just estimates, and the actual number of children on Earth is constantly changing.