It is surprisingly challenging. The mouse doesn't input position, it inputs movement, and not all movement, but movement of a specific point on a plane aligned

It is surprisingly challenging. The mouse doesn't input position, it inputs movement, and not all movement, but movement of a specific point on a plane aligned to itself (not the screen, not the hand) and only if you slide it against a surface, and not your exact movement, due to acceleration and stopping at screen edges. And then it has buttons! And a wheel! And an ominous red light! A good start is to just put their hand on the mouse, put your hand over theirs, and tell them to watch the cursor.