If you reload and it is versatility you want, I would get anything in .30 caliber- 30'06, .308, .30-30. You should have no problem loading them down for the young 'uns. You can even get sabots and shoot .22 cal. bullets out of them.
If it is mainly for the kids it would be a .357 Mag, .44 Mag, or .45 colt. (although I don't think the .45 is available any longer except in the Buffalo Classic.)