If you are interested in going to medical school and becoming a pediatrician, the most important thing for you to do in high school is to take more difficult courses and do well in them. This means the honors and AP type courses. It is not necessary if you start with the very hardest courses either. It may make more sense to take an course of moderate difficulty and "work up" to an AP type course as you become a better student, it depends on how prepare you feel now, whether you start slow and work up or dive right in. It is not necessary that these be all in science and math either, as you will get plenty of science and math as you move through the long schooling that you will need. Medical schools do require specific science courses be taken in college before applying to medical school, but You can actually major in anything you like in college. Still many folks do choose to major in a science like biology or chemistry, for the simple reason that medicine is very dependent on these subjects, so individuals who like medicine are often interested in the sciences, so its a good idea to get a solid science prep in high school, but it does not have to be the only thing you focus on.
Overall physicians need to be able to communicate well, understand people, and increasingly understand subjects that affect health care policy like business and politics, so a broad general education is a good idea, and high grades are a must.