Brother, Sister, iPod--United

Here's a view into the back seat of our Corolla during our morning commute to school. The kids are sharing one iPod and one set of headphones. I thought it was cute, and, hey, it's Friday, so I snapped a quick photo. HOWEVER, now as I look closer I see something that really bothers me--no, not the huge, menacing semi through the back window. No, what disturbs me is the position of my son's seatbelt. How long has he been riding around as a passenger wearing his seatbelt like that? And, more importantly, how could I not have noticed?