Tazman, I too am left-handed and my dad always purchased guns with push button safeties that he had converted for a lefty. Since you want only one gun to fit both girls, I would choose one that has a tang safety. That way, the left-handed child doesn't have to work the safety from the right side of the trigger guard. Savage makes their old Stevens single shot that will probably fit the girls, but it is an exposed hammer and I doubt it has an additional safety. Why not consider other actions besides a single shot and simply limit the gun to one shot at a time? That way you have other options and ultimately a more versatile gun. If you do want a single shot, however, the Thompson Contender in a rifle version would be nice, and you can add other barrels as the need arises. In any event, congratulations on having daughters interested in shooting. Just be careful with the lefty that you don't buy a gun more appropriately suited for her sister.