Two things make “how was your day?” backfire. First, it's huge — you're asking them to summarise seven hours on the spot, so the easiest answer is “fine.” Second, sitting across from you, eye-to-eye, being asked to perform an answer, reads as pressure. Kids disclose most when they aren't the center of attention — shoulder-to-shoulder, hands busy, free to look away. That's why the car, the walk, the dishes are where the real stuff comes out.