Little Joker

Today Joe took Gavin to the pool. It's our neighborhood pool and the two pool houses also contain our mailboxes--right outside, by the pool. As Joe and Gavin were swimming a man came to get his mail.
Gavin looked up and said, "Hi Daddy!" to this man who we had never met!
Joe said, "Gavin, you're being silly. I'm your daddy."
To which Gavin replied in a joking tone of voice, "No. You Gampa!" and then laughed! The man laughed too.
Who knows what he'll say next!