Just to be clear, nearly every (edit: modern) handgun you’ve ever seen, pistols included, is almost certainly a semi-automatic. I’m sure there are exceptions, but AFAIK, any (edit: modern) handgun that’s not a revolver (or something weird like a derringer) is going to be semi-auto.
As someone who grew up around guns (but is not currently a gun owner), and if I planned to buy my child a gun prior to adulthood, I probably would start my kid with a BB gun at a younger age, then likely a revolver before going to semi-auto, but I wouldn’t feel like either of those are choices that are the only safe ones. (If we’ve cleared the hurdle of considering a 15 year old owning a gun to be safe at all.)