The two in the top picture are very flimsy and a waste of money in my opinion.
You're going to want to find the sturdiest tripod you can find that's in your budget. Think: burly, nearly inflexible legs and leg connections.
After that, you're going to want a head that is also rock solid, but is also relatively easy to disengage the tripod head so you can move it around to take a shot, then quickly be able to lock it down again without incurring a shift in point of aim.
Really Right Stuff (RRS) makes unquestionably the best stuff on the market, but you are going to pay a boat load of money for a setup. Maybe in the $1,750-1,900 range new, with the tripod being the most expensive part of the purchase.
Since this is for your son, and the distance may not be that far since you're shooting out of a ground blind (?), it may not need to be perfectly rock solid. I'd encourage you to try and find a big aluminum or preferably carbon fiber (it's warmer to the touch and lighter) tripod from Vanguard with burly twist lock clamps (I've had flip locks break in the cold) and then put a either a Hogsaddle on it (you can probably find a used one pretty easy) or just bite the bullet and get a head from RRS.
If you go with anything besides the hogsaddle (I'm not a big fan of them), you'll need to buy a little arca rail or plate to install on your rifle that clamps into the tripod head like so:
