Read this comic at gocomics.com.
Sometimes with these I think Schulz throws in realistically-proportioned adult objects just to demonstrate that he can draw well technically. Of course Schroeder couldn't actually play the adult piano because his arms are too short; he'd barely be able to reach the keys unless the bench were right up against it.
I notice that, in some of the Sunday strips we've seen, there's a blank spot between a couple of the panels in the bottom row. It's really noticeable because it always seems to overlap two of the panels. Is this the result of some problem with their source documents?