There are three broad categories of Peanuts strips from this time: kids acting like kids, kids acting like adults, and kids displaying precocious knowledge of adulthood. (There are other types, but these seem to be foremost.) This strip falls into the third category, with Violet speculating about later getting a date with a human being who's not yet old enough to talk. Notice, by the way, Schroeder's dubious look in the second frame. That expression is not essential to the joke, but Charles Schulz put it in anyway. This is one of the joys of early Peanuts for me, noticing those little things Schulz just threw in.
Schroeder was an Archetypal Baby in this one. Enjoy it while it lasts kid; it won't be long at all before you become the Archetypal Musician instead.
