Hire a coach to at least evaluate his ability. Get a coach that's over 2200 USCF, just so you get someone that can do an accuate evaluation. Preferably, at least get a GM to at least do the evaluation, then he could suggest an appropriate level coach if a GM rated coach is too expensive.
Arguably, getting the best coach that money can buy is a good thing, but if your son is 1900 on chess com, he'll need an established OTB rating to better understand his ability and better figure out what rating level of a coach he needs.
But an initial evaluation by a GM or FM would be very helpful in the short term. A USCF master or senior master would be sufficient too.
My 11 year old son joined chess kids last month and is already 1900+ . The nearest competition that i have seen on there is 1500 and maybe one 1600. He is learning so fast. When I checked in on him last night he was even playing TWO games at once! On the desktop with ChessKid and on his phone he had what looked like a game going on the lyechess app. It’s quite remarkable.
My question is where do I go from here? Buy him books? Hire a coach?
Thanks