[Content warning: this post has been written while the author is on cold medicine and before having any coffee. Read at your own risk!]

But you know those other kids are going to go right back to being assholes as soon as "the magic of Christmastime" wears off.

It seems like the message is kind of, "It's ok to be an asshole, as long as at certain, 'special' moments, you show a token gesture of goodwill."

I haven't watched the whole show through in decades, so it's possible my memory is faulty, but I don't recall any of the mean kids making any sort of apology or atoning for their behaviour. It's just "and now we're all friends because Christmas!"

And then the next day, Lucy's back to tormenting her ostensible "friend".

The message is that kids are often assholes to other kids, picking one or a few to gang up on. Which is true.

In the Christmas Special, the kids come to see Charlie Brown as right and are fairly vocal about this ("he's not a blockhead after all", etc.). It is somewhat tethered to the religious elements voiced by Linus, which gives the turnaround to Charlie's perspective a kind of cultural weight, i.e., the audience is intended to understand the kids as wrong in some kind of fundamental way. It's not as simple as "the magic of Christmas".

In the Halloween Special, the kids don't do the same for Linus, apart from Lucy who pulls him out of the cold and tucks him into bed.

The dynamic between Lucy and Charlie is a lot deeper than her cynical kicking the ball trick. Schultz uses their interactions (the psychiatry booth, him keeping her on the baseball team even though she's consistently terrible) to reinforce an overall theme that optimism is better than pessimism. Occasionally he directly peels back the layers behind Lucy's crabbiness like when Charlie's in the hospital.

It's easy enough to interpret Peanuts as being that. But Charles Schultz was not trying to present that. He was presenting the world as it is, and how one person can still maintain his optimism in spite of all that. This is made abundantly clear in some of the other strips, like the Father's day strip where he explains to Violet that no matter what, his dad will always love him, and he doesn't care that Violet's dad can buy her all the things.

Schultz was a relatively devout Presbyterian (though still very much a free thinker and criticized the direction American Christianity was going and its attitude about the various wars during the 60s-80s). He was incredibly optimistic about humanity, but he showed in Peanuts the reality of our "default" state, especially among kids.

Keep in mind that these are all 2nd and 3rd graders in the story.