How exactly are you defining the “crime” now? The act of leaving a baby in the car until it dies IS the crime. If that much is proven, the crime is proven. What other circumstances are you suggesting should be present?
It sounds like you’re saying the state should have to prove beyond a reasonable doubt that the parent did it on purpose. Is that what you’re saying? If that’s the case, you’re essentially making it legal, since it would be virtually impossible to ever prove intentionality unless the person confessed to someone.