How do you.....

How do you explain the Atonement to a seven year old? Colby has been asking questions about it very randomly! He said in the car the other day "I don't get how Jesus died for us." Then as I was doing the laundry tonight and he was playing wrestling he came and said again "I just don't get how Jesus died for us, if he died he would be in heaven anyway." I have know idea how to begin this conversation! I'm 30 and I don't have a full grasp on it!