Pack them a snack, to take to school with them, and to eat when school lets out or at recess.
Lunch for kids in school is pretty early.. so between lunch time and 4:00.. it is a LONG time for them to go without food... and I don't blame them for feeling starved. Going so long without anything in them, can also affect blood sugar levels and cause kids to have poor concentration etc.
So a snack is important.
If they are getting out of school at 4:00... WOW that is a LONG day for a kid. I assume this is because they are in an after-school A+ sort of extended care/afterschool program? If so, usually these programs allow the kids to bring their own snacks and to eat them. Kids are super hungry after school... and then at after school programs too.
I would not make them wait until dinner for a "snack." They should be getting a snack, if possible, by having one at school in the afternoon before they come home. Instead of waiting until 4:00 to do so.
At this point, and time, a "snack" is not a "treat" or reward... it is just a pure simple biological need and for their body.
Kids generally DO need snacks... just like toddlers. It does help the body and helps a child from over-eating too or eating junk food.
All the best,
Susan