Do you want a semi-auto, pump, lever, bolt or single shot? Or a pistol?
I currently have a Ruger 10-22 and a browning BLR (lever action). I've previously owned several Remington Nylon 66's and they were fun guns. I also own a few Browning Buckmark 22 pistols and enjoy them too.
It's hard to go wrong with practically any of the 22 rifles or pistols available. Figure out what your son will enjoy and that it fits him for now. If he outgrows it, he can always put it aside for his son or daughter and continue the family tradition. Good luck.