problem solved

I was driving the boys to school today and Alex started asking me about our cars.  Which one cost more money?  (Andy's)  Why? (Because mine was used, Andy's is new and is a different kind of car).  This led to a discussion of the differences in the cars.  Which one had more seating, which one was noisier, which one had the adapter to play Alex's iPod, etc.  Alex finally concluded that he likes Andy's car more than mine.  His reasoning was that Andy's car is cleaner.  I asked him who he thought made the mess in my car, and he completely fessed up that it was him and his siblings. 

Problem solved.