Ruger Bearcat. The single action would be perfect.
Good job on teaching them young. I my little girl was 5 when I put her behind a marlin youth 22. Sandwich bag of 22's on the side. Bipod to hold it up. You would think you just asked her to leave a toy store telling her the ammo is almost gone.
Maybe a Heritage, they rust easy but I picked one up years ago that my dad uses now. He let it rust all to hell but after a little oil and some steel wool it was up and running again.