Set two small jugs on a tray and half-fill one with dry rice — or water if you are relaxed about spills.
Show one slow pour, exaggerating the tilt and the stop. Then hand it over and let your child pour back and forth.
Spills belong on the tray, which is why it is there. When one spills, hand them a cloth rather than wiping it yourself.
Pouring demands graded wrist rotation, bilateral coordination and the judgement of when to stop — the same control that later shows up in handwriting. The tray makes error safe, which is what lets a child keep trying.