Most colleges and graduate schools have advisory and career placement offices that can help connect students with prospective employers or internship opportunities. If you have not yet selected a college this should be an important consideration and something to carefully investigate. When visiting colleges or speaking with their admissions offices it's appropriate to ask about a their programs and placement rates. Some schools have excellent programs and some do not. Once you are in college take time as a freshman to meet and get to know the advisers and others who work in the placement office. Even if you're not able or eligible to pursue an internship until your sophomore or junior year being a familiar face and having a relationship with the advisory and placement staff can give you an edge. In addition to reviewing academic records and resumes, employers will often ask their contacts at the college placement offices for personal recommendations.
Although my background is not in medicine, but in the arts, I would like to give you some ideas. You can start connecting wit the career world of your choice as early as now. Either you, your siblings, or cousins, have or had a pediatrician. Start there! If he/she is a doctor close to your family, reach out to him/her and ask questions about their path, and ask for any suggestions they may have.
Most likely, once you choose your college program, the school you go to will have a department or office which provides professional guidance to all students. They will be a great resource of information to you, once you get to that point in your studies. Medical schools have relationships with local hospitals, clinics, and other healthcare providers, which will in time provide opportunities for you to find internships and practical training.