Why not just freeze the water in the glasses and let it thaw upside down?
How? The glasses are upside down on what looks like a table. I’ve seen this done many times and also pulled the same trick once. The glass is filled. A tray put on top. Hold the glass and tray together and turn it over. Go to a surface, counter, table and place the edge of the tray against it and slide the glass onto the surface. Repeat procedure in opposite when removing water glass. Best thing to do is wait until the kids return, stand them in front of the table. Pick up the glass letting the water spill out. Tell the kids to now go mop it up.