Normally I'm not a big fan of the Daisy Grizzly, but in this instance its probably one of the better options for you. Its a single-pump pneumatic (you pump it once to charge it between shots). Its reasonably accurate (say 2-inch groups at 50 feet). And at a maximum of 1.9 ft-lbs of muzzle energy its not overly powerful. My biggest complaint about this gun is that the valve and pump-seals in the gun aren't as sturdy as more powerful guns so they can (and if my experiences are an indication) do wear out pretty quickly if you shoot a lot and don't follow the manufacturer's instructions for oiling the gun religiously. I speak from experience since I had two of these guns and it took about 1 year for the seals in each to die. Then again I sorta just guessed when I was close to 1000 shots...
The Daisy Red Ryder, in my opinion, isn't a good option. It may have been 30-40 years ago, but the modern gun is extremely cheaply made. I find I'm doing good to keep most of my shots on a soda can at 50 feet with a (relatively) recent make Red Ryder. The spring mechanism causes a noticeable "recoil" or "jump" during firing which makes it hard to keep the gun on target and the BB moves slowly enough that this can and does sometimes affect accuracy. It doesn't help that the trigger is really bad and the cocking mechanism is hard to work. What's true of the Red Ryder is doubly true of the Daisy Buck (an even more cheaply made and less powerful gun).
You might look into the Gamo Recon. Its a springer with around 4 ft-lbs of muzzle energy. Basically its a break barrel gun designed for young shooters. It takes about 15 pounds of force to break the gun open and cock the springs. Accuracy is good, say 1-2 inch groups at 50 feet. Cost is reasonable. The only real drawback I can see to this gun is that it requires a scope.
The same basic commentary for the Recon would apply to the Gamo Delta, Crosman Raven and Beeman Guardian, though all of them have iron sights.
If you don't mind using a co2 power-source, the Crosman 2260 would be a good choice. Its accurate (1-inch groups at 25-30 yards), powerful, and has a reputation for being very durable. It might be a bit big for a youth gun, but it would definitely have room to grow with your son or daughter. The only issues are that its a .22 caliber pellet gun so the ammunition is a bit more expensive than .177 caliber pellets/BBs, that you have to buy co2 cartridges to shoot which adds to the cost per shot, and that co2 guns lose some power/speed in cold weather (below 40 degrees F).
I know you weren't horribly interested in multi-pumps, but there are a couple good options in that category to consider. First the Crosman Recruit (essentially a smooth-bore version of the Crosman 664). The big selling point here is the stock is adjustable so it would be able to grow with your young shooter. Then there's the Crosman 664SB and Daisy 880, which are both accurate, reasonably powerful, and reasonably durable. The Crosman 2100 would probably be a bit big, but its probably the best multi-pump available for under $100.