It's not a matter of how many years.
Did you declare your child when you applied for PR? Did he/she went through medical? If you didn't, then you can never sponsor your child.
If your child was born after you became PR, then the above question doesn't apply.
You can sponsor your child any time once you are physically inside Canada and live there. You will need some proof on how you can support your child (savings/job... etc) but there is no fixed amount stated on IRCC web.