Fun with Pre-Literacy

Now that Nate can identify most letters of the alphabet, I'm attempting to teach him that there is a sound assigned to each letter.  This concept has not yet been grasped.

Mommy:  D.  Da-da-da-da-Daddy.
Nate:  Da-da-da-da-truck.
Mommy:  No, truck starts with T.  Ta-ta-ta-ta-truck.
Nate: Ta-ta-ta-ta-Grandpa.
Mommy:  Grandpa starts with G.  Ga-ga-ga-ga-Grandpa.
Nate:  Ga-ga-ga-ga-airplane!  Ga-ga-ga-ga-pumpkin!

All in due time.