My .02 - I'm an NRA rifle instructor working mostly with my son's Boy Scout troop. Think back; in Cub Scouts we put a BB gun in their hands (Red Rider's). They got comfortable with that. Then we put a single shot, bolt action 22 in their hands. Then, years later, we put a Ruger 10/22 in their hands. At some point they wandered by the trap range and, walking by, got used to the sound of the 20 gauges. Some took to shotguns, some didn't.
The rest, as they say, is history!