Baby teeth decay: how is it treated on the front teeth?

I noticed some shallow brownish spots right on the front surface of my two-year-old son's upper front teeth. They are close to his gums, but they don;t touch the gums. At first I thought they were just enamel stains, but after a closer look and doing some research, I think those are small cavities. I'll be calling a dentist for an appointment tomorrow, but I am very nervous and cannot sleep. How can those cavities be treated if they are so shallow? I think regular fillings could just fall out! Will my son needs crowns? Can the procedure be delayed (by doing something temporary - like a sealer) until he is a little older (3 years old or so)? If he needs crowns, will they have to put him under general anesthesia? We have a medical insurance, but no dental insurance. Would the medical insurance normally cover anesthesia? Than you for your help; I am very concerned.