While it's not inexpensive, a TSS load would be my suggestion. If recoil isn't a concern, there are several loads commercially available in the 1.5oz range and I'd recommend straight #9s. That said, some smaller manufacturers are making TSS loads with a lighter payload, which are designed primarily for waterfowl and generally loaded with #9s. I'd go that route for kids just getting started. That's what I did with my son several years ago with a 28ga and 1.125oz of TSS. That type of load will still be fully capable of clean harvests well past 40yds and comparatively pleasant to shoot.
