We've seen one-use animals other than Snoopy before (a dog and two birds), and we had one strip in which we saw other kids from a distance. But this here is the first time in Peanuts we've seen entirely non-regular character designs as throwaways. Also included: the first kid with glasses, and a kid with a "Jughead" hat.
Note: of all the extras in that sandbox, only two of them are girls, and both are cast members. Also, Violet wears her hair down this time; she's got it in a bob most appearances now.
The tiers of Peanuts characters:
"Cast" characters are the main guys. There are some characters who, once they arrive, are frequently seen for a while. Some of these are long-term characters (like Charlie Brown, who was in the first strip and the last).
We might call "understudy" characters those who join for a little while, like Frieda, but then digress into occasional appearances, usually disappearing completely some time later. Eudora is also one of these, I'd say.
Some never seem to progress beyond being bit characters. These guys are usually introduced as part of a story, and sometimes get used as extras in group scenes. Roy is a good example; he's not quite an extra, and in fact has an important place in Peanuts history for introducing Charlie Brown to "Peppermint" Patty, but he never really joins the main cast. I think "5" and his sisters, the twins "3" and "4," are also in this category. (The digit kids aren't much remembered now, but are notable for appearing in the dance scenes in A Charlie Brown Christmas.)
