As stated already,the .243 will be fine as long as your son does his job and puts the bullet in the boiler room!
You won't see me get torqued up at your statement....I tend to agree!
The supermagnum fad is certainly out there.....before you know it...the .50 BMG will be the "minimum" caliber for deer!!
PS...I'm only kidding!!...The big mags DO have their place,especially when you want to reach way out and get a deer's attention...but you don't NEED a .300 Ultra to kill a deer @ 100 yards.