If you are a US citizen, and your wife and children entered the United States with a valid visa, whether it was four years ago or just recently, they can apply for their Green Card. The legal term is adjustment of status. You have to show that the relationship is valid with your spouse. Proof of a life together and obviously if you have children together, is pretty strong evidence that you have a valid relationship with your spouse.
Where I practice in Wisconsin and in the Chicago area, the process is relatively quick. From the time you file the application, you should receive an interview within three to four months, and your Green Card within that four-month period. If you do find yourself in situation, please contact an immigration attorney to help you through this incredibly paper-intensive process.
John Sesini is an experienced immigration attorney with offices in Green Bay and Milwaukee Wisconsin. If you have any questions regarding these matters, please contact the Sesini Law Group, S.C. and obtain your initial consultation.