Check with your local dental society in regards to any services that may be available to your son in regards to his missing teeth. They may be able to refer you to further resources that are either public or private.
The usual process I would imagine is to maintain the teeth that he has to continue to have a cosmetic smile and something functional. As he gets older, some minor cosmetic work may need to be done to make his teeth appear larger as he will continue to grow but his teeth will have a baby like appearance. If there are problems with them, they may need to be replaced with dental implants or dentures. Dental implants are titanium screws which are placed into the jaw and crowns/caps are placed on top. These implants probably wouldn't be placed in until his jaw has stopped growing or is somewhat stable I imagine. You would need to discuss the specifics with a dentist who does implants. Unfortunately I don't so I'm not sure.
You should consult a pediatric dentist with affiliated and quality dental care at Gentle Dental. You can replace missing teeth with partials and enhance the baby smile.