Sally and Peppermint Patty shouldn't have been in the class.
In every other Peanuts story, Peppermint Patty and Marcie live in another town and go to a different school than Charlie Brown and the main Peanuts gang, but when Schroder is passing out Valentines, Peppermint Patty is in the classroom.
Sally is several years younger than Charlie Brown. She is his baby sister that was born when CB was already school age. Why is she in CB's class at school? Why are Linus and Lucy in the same class when they are also a couple years apart in age?
Yea yea, I know, it's easier to put the whole gang in the same class. I'm just being a stickler for details!