I think that socioeconomical disadvantage occurs in families of all sizes based on the parents' personal histories and ambitions (or lack thereof). My daughter has 6 children, is working full-time, taking classes to gain her Master's degree, owns her own businesses (2 of them) AND has been remodeling her home with her husband. Their children have all the advantages she did in a family with only 3 children. They are financially sound. Because they are not lazy. Their children are clothed and provided for because she is careful with their finances.
Intelligence is both genetic and environmental, so the exposure to a variety of information lays at the feet of the parents and the child's extended circle. My children were in the gifted program at school, though they were children of a single mom. I went to school full-time AND owned and operated my own preschool while they were growing up. Their father was an alcoholic who couldn't keep a job, thus explaining the divorce!
My father was one of 6 children and had a photographic memory and actually skipped 1st grade. My mother was one of 8 children. Together, they did so well, that she never had to work outside of the home. I was raised in a "Beaver Cleaver" type home. Economics only influence the children if the parents allow.
Very thought provoking question!