A few weeks ago, my five-year-old son asked, “Mom, what’s your pebble?” 
“Huh?” I asked back.
“Your PEB-BLE,” he said. “You know, like how my left foot is smaller than my other one…” 
I resisted the “huh?” again, even though I had no idea what he was talking about—pebbles or foot size (his feet are the same size, essentially). 
So I tried [...]