Can you tell me if dentists want kids to get cavities so they would have a lot of fillings to do, thus making a lot of money?

You got it all wrong. Dentistry, as a profession, has tried just about everything to prevent decay in all patients, especially children . Fluoridation, specialized toothpastes ; mouthwashes, and public education all have brought down the incidence of decay over the last 50 years. There is more than enough dentistry to do on adults who ignore their health to keep every dentist busy for a very long time. Think about it.