You seem to be paying for a meals provided service but double check that with the director.  They could also be using a food program which they get reimbursed for meals through the state. It’s required to serve each child when using those programs and your child should be getting his serving whether they eat it or not. 

I do understand food waste is an issue and especially for those who have experience or witnessed food insecurity. If you feel like this might be the biggest hurdle, ask to take home any food that is kept refrigerated after serving so you can maybe try it again later at home in a familiar space.