I started on a Model 7. Difference of a Model 7 vs. 700 is the Model 7 has a shorter action and I think you can get a Model 7 in a youth version (shorter stock). Not sure about a 700. As far as brand vs. brand....well, good luck in narrowing it down. Years ago savage used to be crap....then they came out with this little accu-trigger thingamajig and now people really like them....as far as the Ruger, never been a fan but it's just aesthetics that I'm not a fan of. The new M77s are supposed to be pretty good though; but we're also talking best bang for the buck, under $400 w/o scope right? So, that being said, I would pick either a Remington or a Ruger....wood stock (increased weight reduces recoil), plus with a solid wood stock, you can trim anything to fit (butt, stock, forend, etc.) Can also bed and free float easier than some of the injection molded stocks that come from the factory. Hmmm, what else.
What is making me wonder though is your initial post asked what rifle for your son, who is or will be 12, also mentioning deer in the equation. Then people give their opinions and a lot are around the .243 range, but then you seem to want more power, more bang, more blast.
Here's a little figure. 400 yards (past what your presumed reference yardage would be). At 400 yards a .243 Sierra Game King will have a velocity of around 2100 fps with over 1000 ft.lbs of energy, AT 400 YARDS. Now if you can tell me that aint enough to kill a deer, something wrong with ya
Take this into account as well, just for reference. My longest one shot one kill drop in it's tracks (ethical shot) on an ELK was approx. 650 yds. I think a little over but it's been a while. Shooting 165 grn. Nosler Partitions (Federal Ammo) as I didn't reload at the time. Ballistics on that are....1818 fps & 1200 ft.lbs. at 500 yards....so probably considerably less at 650.
Just a thing that there is no reason for more power when more is not necessary. When I scope on anything, I don't take into account the size of rifle I have and hold off.
When your sons get older, they can move up to what rifle will work. Who knows, if all they hunt is deer, they may keep the .243 or 7mm-08 or whatever and be a freakin' tack driver with it.
Thought I'd mention this as well, if you don't reload, may want to check your local stores and see what ammunition they carry. That's the only reason I would be against the 7mm.