Does it ever occur to you that children in extended families are reaping the benefits of multi parenting skills? In larger families of typically Italian or Spanish origin, where the extended family systems enjoys a healthy respect, children are bound to by just about all of the adult members of the clan. Table manners are attended to by every Aunt and Uncle who may take a passing interest and the children are never left to the devices of one set of parents exclusively.
The average British, Australian or American child is at the mercy of the foibles of one mother and one father. Outside interference with the raising of these children is not tolerated, therefore the child has one set of values; those of the parents.
Well-to-do African families have the same system of extended family. Brothers and sisters interact more closely and cousins are concerned almost with the same affection as a sibling. The advantage of such a system of course is that the children develop in company with so many peers and their social skills are well honed by the time they reach awareness.
Family celebrations command a defect attendance from those who have grown up as part of the extended family system. Refusal to attend a birthday party, baptism or wedding would be considered an almighty faux pas is such society, all good grounding for the corporate social behavior one might expect to be part of later in life. Family duties are considered to be obligations not to be taken lightly and though they should be.
Children of a closer family unit are necessarily not so adept at mingling with others. This is seriously surprising, considering they have so little social experience within the family structure.