Please take my post in the most constructive way possible.
I guess this turned out ok, but there's no way I would have let a beginning hunter take that shot. It's not responsible. He never shot the gun before, I'll be he never shot at a target at that distance with any gun, let alone shooting at something living, the list goes on.
You blame the gut shot on wind?!!? What about the fact that the shooter really had no earthly idea what he was doing? Heck, the wind may be the only reason he hit the deer at all. You'll never know. And then there's your boy being taught to take long shots in windy conditions in the first place.
Think about this, a 7mm zeroed for 300 yds will drop about 50-60 inches at 600 yards, that's 4 to 5 feet. A 10 mph breeze will push a 7mm bullet 2 feet at 600 yds. IMO, If you have to hold off the animal you are shooting too far. I can hear it now, "Aim about 4 feet high and a 2 feet to the left and you MIGHT hit him."
Look at it this way, what if his gut shot ended badly - a lost but very dead deer? How would you both feel then? Would he want to continue hunting? I would hope he'd feel badly but eventually shake it off and continue hunting, but what if he just quit? Bad hits can happen under the best of conditions, why risk it?
IMO, a young hunter should be brought along by folks that set the correct examples. Taking low percentage shots on game animals is not the right way, it shows a lack of respect for the animal. I'm pretty sure you can expect your son to want a 7mm of his own so he can continue to pop off shots and 600 yds and maybe even beyond. Heck, his first try turned out so well.
I know you're a beginner as well, but I think you probably do realize that perhaps it would be better to teach the kid to hunt, so he can get close to game, so his shots are basically slam-dunks. Leave the longer range shooting to the shooting range.