Is Jesus eternally the Son of God the Father? Throughout scripture Jesus is identified as the “only begotten of the Father”.   Is Jesus eternally the Only Begotten of the Father or did He become the Son at His incarnation?  

Scripture to me seems clear that Jesus is eternally the begotten of the Father, which imposes an eternal "family" dynamic within the Godhead.  Do Christians generally agree with this perspective and if not how do they view the sonship of Christ?
The Nicene Creed (Wikipedia: "It forms the mainstream definition of Christianity for most Christians.") answers this question (emphasis added):


  And in one Lord Jesus Christ,
  the only begotten Son of God,
  begotten of his Father before all worlds,
  God of God, Light of Light,
  very God of very God,
  begotten, not made,
  being of one substance with the Father;
  by whom all things were made;