Restoring and preserving a baby tooth is the best way to avoid unnecessary crowding in the future. The last, and I think the most important, reason for fixing baby teeth is to prevent pain and infection. Studies have shown that tooth decay can have devastating consequences that extend beyond the dental chair. As mentioned above, if the cavity is small enough, the pediatric dentist may choose to allow the tooth to repair itself.
This is because saliva can speed up healing processes. Saliva contains proteins, enzymes and compounds that help harden tooth enamel and can even “remineralize tooth enamel.” If a cavity is small enough, a tooth can undergo remineralization (or self-healing) if oral hygiene and diet promote saliva. If the diet is poor and full of sugar and starch, it can and will dominate saliva and cause the cavity to grow. Your pediatric dentist will discuss proper care and course of action if they believe remineralization is possible.
It's a common misconception that baby teeth, due to the fact that they're not permanent, aren't important to care for; but this couldn't be more false. According to the American Academy of Pediatric Dentistry (AAPD), maintaining the health of primary (or “baby”) teeth is essential. They are the framework around which adult teeth will develop. Baby teeth are important for your child to chew on and also serve as a guide for the eruption of permanent teeth.
Early loss of baby teeth creates an open space, allowing other teeth to move to that location, resulting in crowding of permanent teeth in the future.