What is the law about leaving kids alone in the car?

My ex lives in wyoming and I live in Colorado he has cusdody of my 6 year old. I called him before I had to go to work. I was in the middle of talking to my son when my son started to cry and freak out.. Trying to get something out of him what was wrong all he would say is I am scared I am in dads truck. Not getting a clear answer out of him trying to calm him down after about 10 mins my ex jumped on the phone and told me he ran into the store to get a clip for his car wipers... Being a mother living 3 hours away from her son i felt so help less not being able to do anything... I need to know the laws on this...