Most likely it's all three, with a side of public schools' and private preschools' take on the topic.
Abby (in seventh grade) says that they learned about how the Natives helped out and then the Pilgrims gave them diseases and things (I imagine this was in fourth or fifth grade; out here in Salish country the public school does a lot of Lewis and Clark and Sacajawea and Oregon Trail stuff. They try to be fair).
|Lizzy, four years ago.|
You'll notice if you click that link that the negative side of Thanksgiving was not discussed back then, but Lizzy has picked it up anyway. This could be from friends and family (Abby was very vocal on the topic during that fourth-grade year). And it could be from preschool things done at a time other than November; it was a very good preschool.
I tend to celebrate Thanksgiving in the same secular spirit (yes, I know it's an oxymoron) as I do Halloween or Christmas or Easter. To me it's a harvest festival, no more and no less.
Am I thankful? Certainly, and for several reasons. Not the least of which is having been born in a place that at its best tries to be fair... though it fails more often than not.
But that doesn't mean I'm not aware of the unwilling sacrifices made.