I don't have children, but after you have decided what to do, if it includes limiting what your son will be eating, you need to be clear with the church care providers, the MOPS people, and at his play dates, etc. well in advance. If you just suddenly spring a dietary limitation on someone right when they're going to be caring for your child, they'll feel ill-prepared and stressed out, and possibly won't be able to follow your requests. However, if you give them quite a bit of time to prepare, or send along snacks for him and tell them (include a simple list, it's easier to be able to refer to!) what he's not to have, you should be good. If they don't listen to you, reinforce with them why you're making these changes - for his health! If they still don't comply, it's maybe time to change care providers/play date homes.