RE: Caliber for son's first deer rifle?
If any centerfire cartridge is availible to use down to a .204, and you are comfortable hunting with it, use it. Reports to our local and surrounding sheriff departments and throuugh the DNR an estimate of 9 out of 10 deer killed by poaching are taken by rimfire cartridges .17 or .22. Obviously they draw less attention being subsonic and are still fast and deadly.
Of course I come from a state with the highest number of B&C entries in the US, and we are only allowed to use slug guns.