Peaches and Cream Without the Peaches

A few days ago I needed some cream for a recipe, and the half pints were only 50 cents, so I picked up an extra to use or freeze as needed. Well, as I was whipping up the cream I needed, Ellie and Sarah wanted a drink of milk, so to save myself a little work, I poured the milk into the empty cream cartons and told them that this was like drinking milk at school. They liked that idea, and I didn't have to wash any dishes.
Yesterday, I noticed that Ellie had taken one of the cartons out of the garbage and had taken it up to her room. I was glad that she enjoyed drinking "from the carton" and didn't think anything of it until this morning.
My mom just called and asked if I would bring a dessert on Sunday, and so I decided to see if I had all the ingredients to make a key-lime pie (one of which was the last half-pint of cream). Well, I scoured the fridge, but couldn't find the extra cream anywhere. Then I took a closer look at the carton I had found in Ellie's room. It was evident that I had not opened it (It was opened from the back and looked a little bedraggled). I guess that I need to explain to Ellie that cream cartons may look like school milk cartons, but there is a big difference.....although I now understand her lack of appetite at dinner last night.