Always-always begin with the .22 LR
The .22 LR round is a classic starter round to introduce children into the shooting arts. I began with both a .22 rifle and pistol and moved up. The .22 should build confidence in that noise, recoil, and muzzle flash are reduced. They are easier to become proficient at and....and.....AND.....if you buy a really fine .22 revolver, it is something you can pass down through generations of your family as an heirloom. My Winchester model 60 single action .22 has passed, thus far, through four generations of our family, instilling skill, comradarie, tradition, and just plain fun. Go with the .22 FIRST, then graduate to the larger calibers.
Best of luck.