Yes, it is, but how do you prosecute an entire state legislature?
you mean, why hasn't the state made laws against this? they're trying to in MI. any child left in any vehicle, for any amount of time, whether or not harm is caused would be prosecuted. but, like many other laws, if someone is going to do something like leave their child in the car for an hour, they will do it no matter what the law is.
problem does not lie in the legislature, but in the prosecuters office.
besides, if there's a law that says there will be a fine if a child is left in the vehicle, it will make it that much easier to plea bargain down.