Why did Lily and David adopt Vincent?

Lily and David were married in China and moved to America. She had a miscarriage in 1949 and was told she could have no other children. They decided to adopt from an adoption agency in China. They fell in love with a four-year-old boy named Jen. They chose him and began the paperwork to bring him to America. He arrived in America in 1961 when he was six.