It could be that their blood sugar is low from going without food too long.
I would absolutely talk to the doc about this and ask about a blood glucose tester to make sure they are not diabetic.
Make sure your evening snack is a high complex carbohydrate snack. That way it will tide them over through the night better, see if that helps.
We eat dinner around 5-5:30 on most evenings, the kids go to bed at 9pm. We have our evening snack around 8:15 to 8:30ish. Sometimes it is Spaghetti O's or mini ravioli, sometimes it is pizza bites, something substantial that will last.