i'm doing a case study on this at the moment and it's very interesting, it was founded by Alfred Adler a Austrian psychiatrist, it was all generilised basically as all family's are different Eg one trate is a only child will grow to play one person off against another in order to get their own way, this has transcended from playing the mother and father off against each other as a child as this was the best way to get what you want, but if they had a single parent this would not happen obviously. but in general this is how birth order personalitys go.

Birth Order
Typical Characteristics
Only Child

• 
  Pampered and spoiled.
• 
  Feels incompetent because adults are more capable.
• 
  Is center of attention; often enjoys position. May feel special.
• 
  Self-centered.
• 
  Relies on service from others rather than own efforts
• 
  Feels unfairly treated when doesn't get own way. 
• 
  May refuse to cooperate.
• 
  Plays "divide and conquer" to get own way.

First Child

• 
  Is only child for period of time; used to being center
  of attention.
• 
  Believes must gain and hold superiority over other children.
• 
  Being right, controlling often important.
• 
  May respond to birth of second child by feeling unloved and neglected.
• 
  Strives to keep or regain parents' attention through conformity.  If this failed, chooses to misbehave.
• 
  May develop competent, responsible behavior or become very discouraged.
• 
  Sometime strives to protect and help others.
• 
  Strives to please.

Second Child

• 
  Never has parents' undivided attention.
• 
  Always has sibling ahead who's more advanced.
• 
  Acts as if in race, trying to catch up or overtake first child. If first child is "good," second may become "bad." Develops abilities first child doesn't exhibit. If first child successful, may feel uncertain of self and abilities.
• 
  May be rebel.
• 
  Often doesn't like position.
• 
  Feels "squeezed" if third child is born.
• 
  May push down other siblings.

Middle Child
of Three

• 
  Has neither rights of oldest nor privileges of youngest.
• 
  Feels life is unfair.
• 
  Feels unloved, left out, "squeezed."
• 
  Feels doesn't have place in family.
• 
  Becomes discouraged and "problem child" or elevates self by pushing down other siblings.
• 
  Is adaptable.
• 
  Learns to deal with both oldest and youngest sibling.

Youngest Child

• 
  Behaves like only child.
• 
  Feels every one bigger and more capable.
• 
  Expects others to do things, make decisions, take responsibility.
• 
  Feels smallest and weakest. May not be taken seriously.
• 
  Becomes boss of family in getting service and own way.
• 
  Develops feelings of inferiority or becomes "speeder" and overtakes older siblings.
• 
  Remains "The Baby." Places others in service.
• 
  If youngest of three, often allies with oldest child against middle child.

Hope this helps, all the best