^ The fact that two relatively young actors have been cast as Clark's adoptive parents would certainly suggest that his early days will play a significant enough role.
Edit - speaking of which, in addition to the Snyder interview, already posted, this link has some quotes from Lane:
Kevin Costner is 56. He could be the adoptive father of someone ranging in age from 0 to 30. We can't really make any assumption about how much Smallville will be featured based on his age. Not to mention the parents of Kirk and Spock were cast in the last Star Trek movie, yet there was minimal time spent on their childhoods. Until the movie comes out, any talk about how long will be spent on Clark's childhood is pure speculation.