ONLY WHEN I became a parent could I fully appreciate how cruel grocery stores are to display a wall of candy at checkout, just when you're at your most vulnerable—tired and distracted, with no other way out with the kids.

Though I haven't visited any of the Disney theme parks with my children, I imagined it would be like the candy trap times a thousand. Endless temptation. Little negotiating space. A marathon of rejection and guilt. "No, I will not buy you another Ariel figure. No, you may not eat a third cupcake at...