i am a middle child through and through.  my husband is dead center middle of family of 10 kids. our approach to family is eerily similar.  although in large family's like my dh, a new order begins and he is technically the oldest of 2nd half.  i see oldest traits in him too.

my dd is an only, so i can't comment from experience.  but one thing i have noticed in families with just 2, the oldest is highlighted more than the second child.  and i am not talking just about photos.  it seems the oldest is considered more responsible and brighter and the 2nd is perceived as less so and therefore takes more heat from the parents.  not meant to be a generalization, but my dd and i have noticed this in more than just a few families.