How Can Somebody Sponsored for Immigration Include Their Child in the Petition

My brother has an Immigrant visa interview the second week of February 2013 , my dad is a U.S. citizen and had filed a petition on my brother's behalf 8 years ago. Last year, my brother's girlfriend had a baby boy, they don't live together. The girlfriend it seems have no interest on immigrating to the U.S. but has agreed to come just as a visitor. Both want the baby to become a permanent resident. How can my brother included the baby on the immigrant visa? is it too late? Will my brother have to come to the U.S. first and become a permanent resident and then apply for the baby? And what about if later the girlfriend decides to come to live here? if my brother marries this girl before the interview will that affect his immigrant visa?
Your help in this matter will be greatly appreciated.

Normally I might suggest that your father write to the USCIS (if the petition has not yet been approved) or to the NVC (if the petition has already been approved), submitting along iwth his letter a certified copy of the child's birth certificate (with a certified translation if it's not in English) and an explanation of the facts (i.e., that the child was not born until last year and thus could not be identified on the original petition), and ask them to add his grandchild to the petition.

The problem here is that with your brother not being married to the mother and the mother not being interested in living in the United States, all sorts of red flags start getting raised. Is mom really going to return home without the child, such that the child continues to be a resident of the United States? Is your brother truly the father of the child? (Immigration authorities tend to be skeptical of paternity claims where the parents are unmarried.) Given the circumstances you describe, I think it would be sensible for your brother to consult an immigration lawyer.

Married children are in a different immigration category from single children. Marriage can greatly affect the waiting time for a green card. Marrying before getting the green card and failing to properly report it and be reclassified is a major problem.

Your father should consult an immigration law specialist for assistance if he does not understand the process of sponsoring a child's immigration.

Thanks for following up on the "What if he gets married' part....