Some kids are more susceptible to cavities. I never had one until I was an adult. My mother credits our multivitamins.
I would get a second opinion. Worth the $$ to make sure.
You don't need to go to a pediatric dentist either. Most dentists will see kids. I went to a dentist who didn't spend $ on a frilly beautiful office and he did a great job with my teeth at a cheaper rate than other dentists.