I have a new Model Seven CDL in .260. It's fantastic, and I've killed two does with it this season. If the gun itself isn't too large for your son, one consideration is the recoil pad. The CDL, unlike some of the other Sevens, comes with Remington's R3 pad. The recoil feels virtually nonexistent on this gun in this caliber and with the R3 pad.
I don't like the muzzle brake idea because of the added noise. Braked guns are much louder than their non-braked equivalents. Even with muffs or plugs the additional sound is offputting and could discourage the young shooter.
If ammuntion availability is a concern, the .243 would be ideal. Also, a Seven Youth in this caliber likely would not kick bad even without the R3 pad.
Speaking of recoil, I have a Winchester 94 .30-30 and find that its recoil is more uncomfortable than that from my .260 and .308, and about on par with my .280. Whether this is from stock design or what I don't know, but for this reason, would recommend something else.
Regardless of your decision, good luck and safe hunting.
Merry Christmas