Originally Posted by Cat Herder:
Legislation is working on that. 
Scroll up to post 37. They are making it a good Samaritan law.
Good samaritan law or not, if I see a child or animal in a car, I would try to find the adult if there is time, but if time is questionable, I'm smashing.
If somehow I ever forgot a child or animal in a car, I would be happy to come back out and find out someone smashed a window because it was getting hot inside. A window isn't that much to replace. I'd rather come out to see a broken window than a dead child or pet.