SR71,
Well, both rifles are made in Germany. While I prefer Beeman imports RWS are a good product also. The R9 is available in .177 and .20(the caliber I prefer) while the M34 is available in .177 and .22 caliber. Both have two-stage adjustable triggers(I feel the Beeman is better, smoother), cocking effort is 33 lbs. for the M34 and 40 lbs. for the R9. The velocity for both are about the same even though the RWS M34 is rated at 1000(.177) in .177 and the Beeman R9 is rated at 930(.177) don't bet on the RWS having more velocity as RWS is known for using the lightest pellets they can get for velocity data.
As you can see they are near the same so it is going to boil down to preference. Mine is the Beeman. I believe they are a better finished product, just a little nicer and a little more accurate. How big is your son? Is he going to be able to cock either of these rifles? For your stated purpose go with either the .20 or .22 caliber as they are better suited for hunting. Whatever you choose keep us informed on the progress as it takes some time to break them in to get the best accuracy out of a springer. Lawdog