Beaver is sitting in a tire swing which happens to be a white wall tire. In the shots where the camera switches back and forth between Wally and the Beaver, the tire keeps reversing itself from white wall to black wall (backside of tire) several times.
When Beaver is talking to Wally as he is packing some of his things away in their bedroom his top shirt button is opened but later (on the swing and at the table for lunch) it's buttoned up.