"I Love You"

When I was leaving this morning, I went through my usual goodbyes with Sam as he was eating breakfast.
"Bye-bye Sam.  Have fun with your friends today, I love you."  I turned to say something to Chris and as I did, I heard a little voice say back, "I luv -oo."  Sam was smiling at me from his high chair.  After saying it to him on a daily basis, multiple times a day, he has never even attempted to say it.  I immediately melted a little bit and teared up.  It made up for the morning temper tantrum and perhaps even the 3:45am visit that left me in a fog today.

Update: 
The next day when I left for work, I happily said good-bye to Sam, and "I love you," expecting a response similar to yesterday's.  He looked me straight in the eye and said, "Vroomm...."
I tried again, "I love you Sam."
"Vroom."
Chris and I interpreted this as a sign of affection, since Sam loves his vehicles so much.
He has since said "I luv oo," but at random moments.
I guess the unexpected makes it that much more sweet.