In TX it's the law, you can not leave an unattended child even in a running car for the 30 seconds it *might* take to run into, say, the Quik Mart, the Post Office, the bank, whatever.
It's not uncommon for temps in a closed vehicle in TX summer heat to reach upwards of 130-140 degrees! I used to keep a metal bar under my driver's seat when I was in real estate just for the purpose of breaking out a car window if the need arose. Never did, thankfully, but I'd have used it on a pet/child-in-car situation in a heartbeat!
Jan in VA