Looking for youth size Muzzleloaders for my Grandsons, HELP

You didn' t say how old they are but assuming they are around 12yrs I would go with with a lightweight rifle such as the traditions lightning or nef 50 cal.Load light to start them off 50-60 gr powder and a light bullet.Hornady makes a nice saboted 167 gr hard ball that is light so recoil is kept to a minimum.They will love shooting a muzzleloader.