Actually the G-20 was being developed as a .45acp when S&W came out with their 10mm 1006. To keep up Glock shelved the .45 temporarily and changed the G-20 to 10mm.
Recoil is quite soft compared to magnum revolvers, so the only issue little girls would have is the grip size.
Don't get me wrong, I love the 20, had two of them at different times plus a G-29. Great guns for the handloader. In an emergency, they will feed and fire .40 s&w as well.