On a recent trip, I was sitting next to Daughter (age 4) on the plane, eating our dinner, and she looked like she was done with her sandwich. I asked her if I could have the last bite, and she said yes. As I finished it, she got upset with me, saying "I didn't say you could eat it *ALL*!"
I explained to her that "last bite" did in fact mean "all", but it got me thinking. Kids are new to the language. It's more obvious with little kids, but even older kids don't yet have a full command of every expression.
Just one more way that kids require patience and understanding.