Remember When?

You remember when you were excited about going to school?
I mean when you were sad that it was the weekend because you were going to miss your teacher and your friends?
My kids started school last week and were practicaly coming out of thier skins the days before school started. They were lamenting the weekend because it was too long until they could go back to class.
It's actually pretty exciting seeing the joy they have.
I wonder when it begins to change?
What are the predicating factors in that change?
All I know is that we need to foster that joy as long as possible.