The correct answer is a pediatrician. A pediatrician is a doctor that specializes in infant, children and adolescent medical care up to the age of 21. They are trained to diagnose and treat childhood illnesses and diseases including physical and mental conditions. They can also help educate new mothers about healthcare for their babies.
Your audience should probably be adults. If adults learn the healthy habits of eating they can pass it on to their children and friends. Maybe posters or news segments could work to spread the news. This idea could work because adults watching the news segment and Billboards will choose not to pick up that snickers in the grocery store check out but instead trail mix.
Thats all you will need, just elaborate a bit more!