My parents are the same and often say their kids are starved when they get home, but snack is at 3:15 and I try and make it a tad bigger than morning snack. However they have an hour to an hour and a half of free play till the parents come, my kids play hard! I find by thurs, Friday my kids are exhausted not to mention me even after their nap. They need to have their childs supper ready when they get home and the first thing they do is feed him. Who cares about them. I bet you'll find he's exhausted and should be in bed at 6:30 ish if not earlier because he's had such a "big" day! So of course he's hungry and tired dad, we've had a big day. You would be too!
The other issue could be a growing spurt, he's probably eating constantly or drinking milk constantly at home. You could always try milk before he leaves that is filling for him.
Another issue, my daycare kids are very rude and crabby and crying 2 seconds after the parents walk in at night. I always find that interesting. They are angels for me all day then the parents walk in and it looks like I'm a big meany all day cause they just break down and cry. I say to the parents "never cries with me, sorry." Attention attention, they know how to get it! I can't even talk at the door with the parents because the child is being so disruptive and rude. I try to calm them, but it doesn't work, so I talk to the child the next day and say how are we going to greet mommy at the door tonight, and we work on arriving "protocol". It has worked for me.