Are they old enough to stay home alone?

As I mentioned before, we had a fun library day last week. We had made plans to hit the library and then run to wal-mart to pick up a few things and then head back home. Well, we had some unexpected fun at the library (you can read about that here) so it took us an extra long time. Since we have completed our curriculum and school is out for the summer-YEA! that is if school is ever really out which I don't believe it really is when you homeschool. you just may not do curriculum type work everyday but the learning never stops:) -we checked out some extra movies(our library has several feature films for families and if you have never seen Summer of the Monkeys we ALL recommend it). So anyway, as we are leaving the library and the kids are discussing which movie we are gonna watch first, Kalysa says "Mom, I really don't feel like going to wal-mart now. Can you just drop me off at the house on your way?" My six year old asks me to drop her off at the house-which is empty, mind you, since we are all together and daddy is still at work- and she says it like it is an everyday thing. Like she just totally expected me to say "sure honey" and drop her off. Could someone please tell me when my baby grew up and where was I exactly when it happened?!