How do people keep their cars clean?

I have 2 small children. I do not let them eat in the car, I clean out the car every week, and it gets messy again in a day. There are Cheerios on the floor, Gold Fish crackers in the car seats, crumbs on the car seats, and random old receipts on the ground. I have a 4 door sedan that I bought not even 6 months ago and it has gotten progressively more messy in that time. <br><br>The car has more crumbs in it now than most of the homes I have been in. How do people do it?