Personally? I think teenage boys treat food like a plugged-in vacuum treats dirt. Teenage boys could probably eat $600 worth of groceries in a week!

Haha, but seriously, I think he needs to keep in mind that when people go grocery shopping, it isn't all just groceries. Soap, razor blades, toilet paper... the little things that people use regularly add up pretty quickly. Perhaps it would help if you saved your receipts, highlighted the things that he specifically asks for, and tell him how much only his things cost per month, just so he can get a general idea of the cost of what he individually is asking for, let alone the needs of his growing children?

Also, clearly you wouldn't need to spend that much on groceries if they weren't being actively used! The necessity is very obviously there.

Okay, so you have a family of five. Let's say each person eats three meals a day, perhaps with two to three smaller snacks in between. Let's also say that each of those meals magically costs around $5 to purchase the ingredients for. October has 31 days. So, for October alone, if you have three $5 meals a day, it's 3 x $5 x 31 = $465. When you take additional ingredients into account (because I can't recall spending $5 on a full family meal that wasn't fast food), on top of snacks, on top of paper products, hygeine products, garbage bags, and all that other stuff...

You're lucky if you only have to spend $600, I'd say. He's being pretty unfair for someone who doesn't do any of the grocery shopping.