Put a half-full cup on a small tray and mark a short route across the room — from the table to the sofa.
Show one slow walk with the tray, eyes on the cup, feet flat and unhurried. Then hand it over.
Spills are part of it. Hand them a cloth, refill, and let them go again. Lengthen the route only when the cup arrives full.
Carrying an object that punishes sudden movement forces the whole body to slow down and coordinate — core stability, grip and gait all at once. The water gives feedback no instruction can match: it either stays in or it does not.