What are the steps in becoming a pediatric dentist?

Very briefly: I'm not certain that graduating with a baccalaureate degree from college is an absolute necessity, but even in my day the vast majority of dental students have graduated college before entrance. You need not be a science major, but a significant number of science courses are required, so most entering dental students have majored in the physical or biologic sciences.
Dental school generally takes 4 years. Training to be a pediatric dentist requires successful completion of either a postgraduate program or residency in pediatric dentistry which on completion makes you eligible to become certified by the American Board of Pediatric Dentistry.
Then the real work begins. ;-)
There are also many modes of practice. Traditionally this has meant private practice, but for more and more dentists (as in medicine) other types of practice exist--whether in academia, as part of a larger group practice, practice associated with a hospital or medical center, the armed forces, or other public or private agencies.