My son is five feet tall and weights 85 pounds, giving him a BMI of 16.6, officially “underweight.” Yet after visiting his dad he comes back convinced that he’s “getting fat,” a view his father astonishingly shares. (Not too long ago his father causally mentioned to me in front of our kid that “Alex is getting a little pudgy.” It was absurd.)

The other day, my son and I were in the grocery store and I went to grab a pint of my son’s favorite lowfat frozen yogurt.

“No, mom!” he cried, agonized. “I’m getting fat.”