I just came across this app called Remember The Kids.

Remember the Kids is an automatic no-hassle reminder app for your phone to help you remember your child in the car seat and protect from automobile heat exhaustion or hyperthermia. Through your phone’s Bluetooth and/or Automatic Driving Detection, receive alerts when you arrive at your destination, providing you with more safety and security. There is no equipment to install or required changes to your daily routine. Simply install and open the app to immediately gain an additional measure of security that the health and future of your most treasured assets are protected.