I guess I'd ask how old is your son (how big are his hands), what you want to use it for (plinking, learning about shooting, training on a pistol, trigger squeeze on a revolver practice, etc.).
That said you can't go wrong with any of the suggestions -- Ruger, S&W, Walther, or any big name. Do a bit of google research and read some reviews.
When I looked for my 12 year old grandson, the Ruger Wrangler looked good (not really expensive). I'd say a Mark IV was a bit "advanced" for a beginner in terms of price and function, but he will grow into it; and you might look to see if any of your existing guns has a .22 conversion ala my Sig 220.
Another thought is a Sig P250. Double action only (but the smoothest trigger on any pistol I've held) and if you get it in .22 you can simply buy the barrels and mags to upgrade it to .380 (a bit rare), 9mm (very common) and 40, plus the frames come in very compact, carry, and full size and they are very affordable.
Problem I had choosing a .22 -- too many good choices. We settled on a 16 gauge Remington shotgun for slugs as he needed a deer gun more than a .22. If I were buying him something new, it would have been a Sig P250 in .22.