As of right now, Missouri law only persecutes drivers if they leave a child alone in a vehicle, and that abandonment injures the child or causes their death. Specifically, the act is classified as a Class A misdemeanor if the unattended child is 10 years old or younger and experiences an injury while in the vehicle alone. If that injury is fatal, then the court will upgrade the offense to a Class C felony. It's never smart to leave a child in a car for any period of time. The most prominent concerns are extreme temperatures. If the car's cabin gets too hot and your child is restrained, then they could suffer a heatstroke. They could also become injured by being exposed to frigid temperatures for too long. Simply cracking your window isn't enough. The cabin can still become uncomfortable and unsafe, so always remember to check your back seat before you leave your vehicle!