Thanks very much for the advice RavynFallen. They have now had 2 swims in warm shallow water in a warm room, followed by towel dry and drying with hair dryer. Very successful and they just love it!
Thanks also for the warning about the styrofoam. Actually we have lined the styrofoam bin with clear plastic sheeting for easy clean-up, and so far it has been impossible for them to reach the actual styrofoam. But we'll definitely keep this in mind for the future! And we love the back up and 'clear' pose - too true!!