The .44 mag is perfect for your son. A long shot going in? The .44 mag is good to 125 or 150 yards.
If you haven't already shot a .45-70, then I would not buy one for yourself until you have fired a box or two through a friends rifle at the range. You may find that you really don't like it.
At the short distances you are talking about, and out to 200 yards, the .30-30 is MORE than enough to kill any deer, and it has a flatter trajectory and much less recoil than the .45-70.
The concept that you are going to get a big bore cartridge to break through twigs or brush and continue in a straight line is simply false. Time and time again, tests have been set up and published in the big shooting magazines, showing that all bullets deflect when they hit brush. (Most of the articles are entitled something like, "Breaking the Brush-Buster Myth."
No ammunition makers advertise their cartridges as being able to "cut through brush." Even those that make the big bores. Why? Because it isn't true.
If you will be hunting from stands, then you will have lots of time pre-season to simply clear out pockets of brush around the stand, creating several shooting lanes or shooting pockets in the brush. That's the right way to do it.
It would be really terrible for your son to try to shoot through brush, and badly wound (and lose) his first deer. Tragic.
Also, at the distances you are talking about, I would keep the scope at 3 power.
Just my thoughts,
Mannyrock