The Crosman 2100B seems like a pretty good deal. It has a rifled barrel. I personally wouldn't shoot BB's out of it....not good for the rifling, not to mention at the velocities that rifle is capable of...some nasty ricochets. Don't shoot your eye out...like Ralphy.
One thing to keep in mind, CO2 is temperature sensitive. The colder the temperature the lower the velocity and number of shots from each CO2. Considering your son is 11 years old, I would stay away from the break barrel guns, he might not be able to cock them. Also they take a lot of practice...
gregkl......check out Midway USA they have some get deals on air rifles. The have a Stoeger .22 cal with scope and a built in suppressor for $99.95, it's at least $150 everywhere else.I have one and it works great. Remember though...like most breakbarrel rifles it requires a couple hundred round...
I agree with the airgun section idea. I have been shooting them for a number of years. Shooting break barrel airguns is more complex then people think. You must select the right pellet that works accurately in you gun....then there is break-in time before everything settles in, not to mention...