I would overwinter the lilies in whichever pond stays warmer. If you wanted to try overwintering them in the kiddie pool, I would wrapping insulation or something around the outside to help keep the water warmer. You may also want to consider making a PVC/plastic sheeting coldframe over the kiddie pool to keep the water temps higher. BTW, Gypsy is a hardy but probably would fair well with the trops to get it better established.