Children don't exercise. They run the last twenty metres to a gate for no reason anybody could state, hang off a railing, and then complain bitterly about being made to go for a walk.
Somewhere in the intervening years movement got reclassified as a debt, with a monthly fee and a permanent sense of arrears. The body never agreed to that reclassification. It still improves for hours after any movement at all, still fails to distinguish between a proper session and dancing in a kitchen while the pasta boils. Grace here mostly means unsupervised.