I have 2 boys, now 10 and 12 that started shooting .22LR pistols at about 6. I went through most of them mentioned and settled on the .22/45s from Ruger. Better triggers, can be improved, great aftermarket support as well.
The SIG for instance, they both hated it. The trigger pull was terrible, sold it, same for most of the rest. The Buckmark and the Ruger 22/45 are my go to choices for youth.
The suppressor goes on a few models of the 22/45s. While I have a light and a standard with threaded barrels, they shoot the standard better than the Lite, so I would go that way. At 9 and 11, they shot in the Ruger Rimfire Challenge both regional and Worlds with these and an AR22.
Bring him to the NSSF Rimfire Worlds in Arkansas the first week of October. Very youth friendly competition and we will have some Pro Clinics at the Friday evening shooter reception.
Good on you for teaching him!!!