The card game Charlie Brown and Patty are playing here is probably Bridge, a game we hear Schulz was devoted to around this time.
As time passes, there are two types of character roles generally in Peanuts: those who we are expected to empathize with and those we view from without. Charlie Brown is nearly always someone with which we are to identify with, but with other characters it varies. After she settles into her role of Resident Crab Lucy, a force-of-nature type, is viewed from outside. Linus can play both roles, the former when interacting with his sister, the latter when playing the part of inscrutable wise kid. It's the difference between having a three-dimensional character and a two-dimensional one: both are actually necessary, but it can be troublesome to have all one or the other. (With three dimensional characters, it is easy to have them come out bland and wishy-washy. They tend to need elemental, two-dimensional characters to bounce off of and define them.)
Patty and Violet seem to be used more as persecutors for Charlie Brown later on, but here she and CB are used identical roles.
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