Are you like your mom or your dad? My maternal and paternal sides differ in size by a great amount. On one side I have 2 aunts/uncles and on the other, I have 10. Now every human is a three dimensional person. Some may not be deep, but everyone is a round character. In a small family, it seems people are quick to slide a child as 'so much like their mother/father' despite said child not being like the referenced parent. It may take several trais, but that child is the one that is like X parent. To borrow a phrase from Malcolm "Ugly MFer" Gladwell, this is a form of thin slicing. We take a small amount of data and make a decision. This is a poor application of thin slicing as it usually is wrong. It seems that over a longer perod of time, a real clear cut X child is like X parent can be determined. Sometimes there is no match. My mom and her siblings don't really fit with my grandparents.
In a big family, that isn't the case. There is the definite heir to a specific parent. Since all of the children grow up in the same environment, you really get a view of genes at play. On my father's side, there is a definite heir to my grandfather and heiress to my grandmother. It's not even close. No one disagrees. It's even a good family joke about my uncle being the reincarnation of my grandfather once he hit 50. Had someone viewed the family fifteen years ago, they might have made a different decision about my aunts, saying that they all were pretty similar and there was no true heiress. An observer might have guessed the uncle-grandfather similarities, but it would not have been as clear cut. With a large family, I don't think outside observers are as quick to make a snap judgment on who is the 2nd coming of which parent.
As a tangent to this idea, a big family makes it easier to figure out where the bad behavior genes come from. Families with only children or two kids make it tougher to see who brought the bad DNA to the show. For all the ripping on irresponsible single moms, if they give birth to that one child and dad leaves the picture never to be seen by the social circle, how are we to know if it's an issue of mommy being bad or the sperm donor being a jackass? This may give some single moms cover as they can blame everything on the dad, wiping their responsibility clean since they are sacrificing to raise that kid on their own.