Baby teeth, grown up teeth, and wisdom teeth. Your teeth change throughout your lifetime. There are 20 primary or baby teeth that are usually erupted by 33 months. Those same teeth will fall out or shed starting at age 6 until age 12. Primary teeth are given letters for names while adult teeth have numbers. The total amount of adult teeth can be 32 if you have all your wisdom teeth or 3rd molars. Is it important to keep baby teeth? Does it hurt to just leave cavities in baby teeth alone?
Baby teeth are needed for chewing food and permanent tooth development. They provide a nice smile and promote a good self-image for children. They are needed to speak clearly and some words like "that" are hard to say without them. If they are lost too early, then permanent teeth can come in crowded and out of alignment. And cavities left in baby teeth can cause unnecessary pain or even an abscess.
The Illinois Department of Public Health has information on the causes of early childhood tooth decay found here: https://dph.illinois.gov/topics-services/prevention-wellness/oral-health/fast-facts-oral-health/early-childhood-tooth-decay.html
And for a fun video on how to brush and avoid cavities for kids click on this: https://www.youtube.com/watch?v=hDZXSMU2lAk