I appreciate ur effort to get the kid treated and I also appreciate the efforts of the dentist who tried to stop the progress of the condition. I cases of early childhood caries in most of the cases there will be sub surface demineralization which makes the tooth very weak. When the tooth is weak it cannot withstand the forces of biting. Most of the times it requires a full coverage crowns followed my meticulous maintenance. Meet a pediatric dentist and get the treatment done. 3 yr old suggests ur kid may be in a pre-cooperative phase.

It's need to maintain proper oral hygiene, avoiding carbohydrate rich food. Teeth which r decyed kindly restore it if not put temporary crowns.. to avoid decay diet n item hygiene is very important

Seek an opinion of pediatric dentist to get the best opinion and treatment

can place strip crowns or celluloid crowns for anterior teeth as they act as bulk filling and can stay for longer time

Good oral hygieneMeasures you are taking for your child, if restorations are not retaining on teeth, let them as it is or go directly for temporary crowns,, because front teeth will be shed off by his age of 6-7 , continue with your hygiene, its enough