If you're the son or daughter of a US Citizen the first thing your lawyer must do is analyze the facts to see whether you might already be a US Citizen. Through the years we've had many people come to us to get visas or residence only to have the pleasant surprise that we could get them a certificate of citizenship instead!
Still, in most cases, a son or daughter of a US citizen does not automatically get citizenship and so needs a parent to petition for their green card.
If you are not married and under the age of 21 when you file you are an Immediate Relative of a US Citizen. That status will often give you an advantage in getting your green card. There's no waiting list for Immediate Relatives of US Citizens, and certain bars to adjusting your status to residency in the United States do not apply.
If you're married or are over 21 you can still get your green card. However, there is often a waiting list involved, and the rules tend to be somewhat stricter.