The Moon’s diameter is a little over one quarter of Earth’s mean diameter. In the scene both disks remain visible, making this a useful first comparison before exploring larger differences.
Make a miniature pair
If Earth is a 2 cm marble, the Moon is about 5.5 mm across. That describes the sizes alone. Their real separation is not represented by the gap in the scene.
One ratio, two perspectives
Swap the objects to make the Moon your marble-sized reference. The physical ratio stays the same, but the miniature Earth grows to match your new starting point.