Atash,
Is this the first time that you and yours will have handled a gun? If so, I recommend starting out with a .22 caliber. The reason is that the diminutive nature of the .22 caliber will allow you to focus your attention on how the gun feels when it is positioned correctly in your hands and feeling your body position in relation to where the hole shows up on the target without being distracted by recoil and noise. If they will let you rent a .22 with a silencer on it, all the better. Buy a .40 caliber glock (model 23) and just let it sit in your closet for a while. In the meantime, rent a .22 and put a couple thousand rounds through it over the course of a few visits to the range. I think that would be good training for your unconscious mind. All animals react with alarm to sudden loud noises. Humans are no exception. If your unconscious mind's first experience with a gun is such that it does not trip the unconscious alarm system, that will go a long ways in preventing you from developing a "flinch". That's a reflex that all shooters develop over time. Your nervous system learns all by itself that squeezing the trigger results in a sudden, irresistable upward lift (recoil) so you wind up developing an involuntary reflex that seeks to counter the recoil by pushing the gun downward as you squeeze the trigger. This results in a phenomenon known as "missing". If you can establish a baseline sense of normalcy in which recoil does not trigger the startle reflex then you will be ahead in un-training any flinch you develop in the future. Another nice thing about the .22 is that you can go to the range and shoot a 500 round brick without ripping the wallet off of your ass.
