It is a very common practice, but you need to meet several requirements:
At the time of the first visa application, children must be younger than 18 years old. When you extend your current visa, it is possible to include children who have already turned 18 after the first visa was issued.
Children must be financially dependent on and live with you.
If your spouse or partner has a child from the previous marriage(s), you must be able to provide documentary evidence that the parent takes all the responsibility for the child’s life and well-being.