Every hour, a child is hospitalized because of a gun. Every other day, a child is killed by gunshots. The staggering statistics, compiled by ABC News, are part of a new “20/20” investigation into youngsters and guns — and how to prevent them from shooting themselves or their peers. An early preview of “Young Guns” on ABC’s “Good Morning America” shows how curious kids will find, and play with, guns if they find them. After telling two young boys to yell for an adult if they find a gun, a child psychologist leaves a playroom where the youngsters’ every move...