I think I am a bit more leanient on this topic of food.
Today we had hot dogs for lunch (it was a quiet movie day and I didnt feel like the hassle of a big lunch and thought everybody liked hotdogs (as they did last time we had them)
4yr old girl decides that she no longer likes hotdogs. no problem, my son ate hers and I made her a peanut biutter sandwich.
I have no problem with kids not liking something, and I do offer to make up a quick something else for them. I dont care if they dont eat their veg I offered, but I do always offer a vegetable with every meal and/or snack.
Alot of food gets thrown out here, and I wish I had a dog to eat the scraps!
I couldnt be bothered fighting with kids to eat their food, thats just me. I never offer a treat or dessert here, so theres no real reward to finish their meal. The odd time I will re-serve their lunch in place of their afternoon snack if they didnt touch it and I know for a fact they like the lunch I served.

I agree that for the 3 months they are here, whatever, praise the kids who do finish their plates, and hope they dont notice when others dont!