The F Word

I was chatting with the daycare teacher at the edge of the playground.  My son who was about 7 years old at the time was busy playing with friends at the far end and had not yet noticed that I was there to pick him up.  We had been talking about the kids for a few minutes when we heard my son call out with excitement "Dad, I know the F word!"  
I heard the teacher gasp and could see a sudden sense of panic on her face.  I began to shout "We don't say that word!  Don't say that word, don't say it!."  My son didn't hear anything I yelled.  He was too excited to tell me the news.  He was running straight towards me with his fists clinched and his arms pumping like a sprinter.  All the way over he was announcing at the top of his lungs "I know the F word!  I know what the F word is!"  I kneeled down and spread my arms out to greet him while trying to keep him from blurting it out.  He ran up and grabbed my arms rather than giving me a hug like he normally would.  I was still pleading with him not to say it but he talked over me.  
"Dad, the F word is Full. The F word is Full." 
"Huh?  That's not... uh, yeah, Full is an F word."
He must have sensed my confusion.
"You, know.  In the car, there's that pointer thing that has an E and F.  The F is for Full."
"Yes, you're right!  Full is the F word."