People Suck

I am just venting at the moment. But people really suck!
I took my 10 year old to see the Hannah Montana movie, which by the way was pretty good.
Once the movie was over, we left. She went to the restroom and then realized that she had left her purse in the seat.
She ran back to the movies, we had only been gone less than 5 minutes...And her purse was no longer there. The cleaning crew was already there and had yet to get to our row. They helped search with the flashlights...but no purse.
She didn't have much in it, about 10 dollars. But talk about devastation and a life lesson learned a little too early.
She is so upset with herself that she forgot it, but more devastated that someone would actually take it.
How do you explain to a 10 year old all the negativities of the world? They know its not perfect, but you don't want everything to be horrible at the same time.