How long does it take to get a green card after being married for 11 years and have 2 children who are US citizens?

If you entered the US lawfully, your spouse could petition for you and the process would take about 4-6 months. If you entered the US unlawfully, you cannot complete the process within the US under the current immigration laws but would have to go back to your home country to consular process and departing the US would cause you to trigger an automatic 10 year bar to reentry, which can only be waived by a showing of extreme hardship to a US citizen spouse, which is fairly difficult to do in most cases.

That would depend if you came to the U.S. legally or illegally and whether you are inadmissible on other grounds.

That depends on whether you entered after inspection or permission e.g., visa; or illegally. If illegally then the unlawful presences has to be waived; If on visa, depends on the type of visa which may also require waiver. However, if your US spouse filed a petition before Apr 1, 2001 then you would not need a waiver for unlawful presence but rather pay fines.

If you are eligible for adjustment, it can take 6 months. Consular process takes about 1 1/2 years. If you entered the U.S. lawfully or had a labor or family petition filed for you on or before 4/30/01, you might be able to do adjustment without leaving the U.S.

Eligibility and processing time depend on whether you entered the country lawfully. If that is the case, you should have your green card within approximately 3 months. It takes otherwise a careful review of your immigration history to determine whether you should apply and how long the process might take.