Why is the study of developmental psychology important?

What do developmental psychologists do?

Sorry, we don't do your homework here.
See: https://www.askmehelpdesk.com/arts-literature/announcement-font-color-ff0000-u-b-read-first-expectations-homework-help-board-b-u-font.html

NeedKarma,

You got to be joking?
I am 80 years old nearly!
I would not mind getting simple
Answers to my queries.

Rolcam.

Your age doesn't matter. The questions you ask are incredibly generic and are the basis on any introductory textbook or material based on the subject. Plus a simple 5 seconds of googling the exact phrasing would give you the answer.