I don't give them a choice LOL. In my case all the kids in my care are 12-15 months old and have only ever been in MY care. I give them everything. Some days, chicken strips and veggies for lunch, other days leftovers like chili, curry chicken, pasta, etc. I just stick it all on their high chair trays and after mealtime they get down and wait until snack.
I would do the same with the older kids. Tell them that there is a new rule in place, "Get what you get and don't get upset" every meal try including something you know everyone will eat so at least you know that the picky eater is having something.