ORIGINAL: zrexpilot
.243
Just dont use it, cause you will buy yourself one, many dads have switched to the .243 after using the one they purchased their son, daughter, wife etc.
I'm one of those dads... Bought my son a Remington Model 7 .243 for his 12th birthday. Loved shooting it when sighting it in. A couple days later, Bass Pro had a great sale on .243 Model 700's. My .30-06 has been gathering dust since.
BigKoz: Not sure how big your son is. When I was 15, I bought a .30-06, and it was a bit too much. I've been dealing with a bit of a flinch while bench shooting ever since. The .243 is much easier on the shoulder, and, at least for Texas sized deer, it works just as well as the .30-06 did.