As we homeschool our children they will make big decisions about what they want to do in their adult lives. My daughter always wanted to be a veterinarian. So she found a veterinarian she could volunteer for and spent several years working with them. The hired her and helped support her throughout her college education as she studied. Today she is a practicing veterinarian in the same practice and loves her job. She made those decisons at a very young age. We helped provide her with opportunities to learn and she has excelled.
If your child wants to work in the human medical field getting experience is a little harder. They can become candy stripers at the local hospital and this will introduce them to what being around sick people is like. Or work in a nursing home as a volunteer. But a good foundation in human science will help them in their future studies. I found this course on Human Anatomy and Physiology. It is very short and will give them a good basis to start from.
Yes, your child may very well change directions many times in their younger years and explore many different options. This is a healthy approach. I have changed types of work several times in my adult life and have found each new experience rewarding and fun. Help them to explore and learn. Guide them to experience many different fields as their desires become known and the will grow up to be awesome!