Hi Meredith,
If you expect your son will mostly eat off your plate rather than order his own meal, the Disney Dining Plan might not be your best option. Every person on a reservation is required to have a meal plan; there is no opt out choice. You would have to purchase a meal plan for your son even if he did not order many meals.
Walt Disney World takes food, especially healthy options for children, way beyond typical theme park fare. Chicken fingers and hamburgers abound as choices for children, but so do whole wheat pasta, grilled fish, and baked chicken. At buffets, kids have the same bountiful array of choices as adults. Before you rule out a dining plan, take a look at some of the kid menus in
Dining. Click on any restaurant and you will find an option to view a menu on each dining establishment's page. After reading a few menus you will have a better idea about whether your son will want to order his own meals or share with you.
Please contact me again if want more information about dining plans, specific restaurants, or any aspect of your upcoming WDW vacation.