Amina is the mother of Abdul Wahid's baby, and the baby in question is George, who is now six.
Amina, being of a different generation from Abdul Wahid's, reacts to racism differently. Mrs. Ali quietly tolerates the racism in town. Amina lashes out against it. She is very defensive: she sees many people as "bullies" (11.70)—which they just may be—and she believes it's her duty as a mother to teach George to stand up to bullies. She causes a scene at the beach and an even bigger scene at the country club when she mishears "service entrance" as "servants' entrance," snapping, "no chinless flunky in a bow tie tells my son to wait by the servants' entrance" (11.55).
She also has a different view of marriage. Mrs. Ali marries the Major at the end. Amina does not marry Abdul Wahid. She has a change of heart, realizing that she can't work in a shop every day. "I'm a dancer. I need to dance. […] Better to break both our hearts now than watch them wither away over time" (25.76). Perhaps she'll come around later in life, or perhaps not. Whatever makes her happy.
The good news is that she doesn't take George away from his father: she stays close enough that Abdul Wahid can see him. The bonus here is that Mrs. Ali and the Major can see him, too. With Roger being the failure he is, it's not like the Major is getting grandkids anytime soon. The Major may be awful at dealing with Roger, but he is good at dealing with younger children, like George, playing ball with him and offering to teach him how to play chess. It's another way for the Major to retain a little bit of his youthful enthusiasm.