Here's what I have always done for my 1/2 dayers over the years. When they get home it's lunch time, but they claim they "aren't hungry"...although the mood tells a different story.
Get a cute divided plate. Target always has them. Call it a "snack plate". No pressure to eat a whole meal.
Put anything and everything you can on toothpicks. Kids will eat anything with a toothpick stuck in it. Amazing.
No big sandwiches...just little healthy snacks.
Works every time.