DEFINITELY a single-shot .22 rifle or shotgun!
First, I'd like to explain that not only was it the way I was introduced and trained in the shooting sports, but the way that several hundreds of young shooters of my acquaintenace were taught in the boy scouts, youth clubs, campings, outings, etc to the wonderful world of shooting sports. I am a former junior and senior high school teacher and camp counselor and have helped train many youngsters to become responsible gun handlers.
A SINGLE-SHOT OR BOLT ACTION REPEATER is the one to select!
A second choice would be a pump-action or lever action .22 repeater.
1. A first rifle should have the versatility of shooting shorts, longs, and LR cartridges. Minimum noise and cost for the .22 shorts and .22 CB caps. A semi-auto is awkward to use with low-power ammo.
2. There is definitely something to the deliberate mechanical motions required to fire that first shot that makes an impression on young shooters. The handling, loading, and working of a mechanical action is a big part of training the youngster, helping to develope his eye-hand coordination. A big plus is that it helps him to develop the mindset, if you will, that he has deadly force in his hands and that he must always be in full control of it.
3. Marksmanship training is of secondary importance to safe gun handling. The shooter must master the elements of position, sight alignment, trigger and breathing control, etc. A single shot gun forces the shooter to CONCENTRATE on making that shot count, whether the target is a tin can, a bullseye, or small game to put on the dinner table.
4. Ownership of a semiauto .22 LR allows a new shooter to skip many of those constant reminders, and it's too easy to develop a "spray and pray" attitude toward shooting. We've all seen many times where youngsters (not mine!) were handed a brick of 500 .22 LR cartridges and a semi-auto to shoot, they came back 20 minutes later and asked for more ammo! Now, that is not only economically unsound, but just ask yourself WHERE did all those projectiles GO if the shooter fired so quickly and reloaded too?
5. In survival/military training, primitive tools and weapons are provided provided to force the trainee to THINK and develop tactical and stalking skills. Frontier woodsmen types had to develop their survival and woodcraft skills because they had primitive tools!
Enough of the lecture circuit. Make that first rifle a single-shot or a manual repeater!
HTH
John