Something worth to think about!
In case you do not know yet the documentary „Taste the Waste“, you can watch here a 29 min short version „Essen im Eimer“. It’s worth to watch this,actually it’s on a page called „planet schule“ (Schulfernsehen) and I think it should be shown in schools. From grade 3 or 4 on, kids could (or better should!) watch it, I think. We had some very interesting discussions with our kids some years ago when this video was released:

http://www.planet-schule.de/sf/php/02_sen01.php?sendung=8459