I think it is very valuable for young people to recognize that many adults who are good on the whole have some significant flaws. Categorization of people as good or evil works only in the most extreme cases. Most good people they encounter will have short-comings and weaknesses. Seeing this in children’s literature can help people cope with it closer to themselves. It also lets people recognize that there may be some good in a person whose behavior is on balance bad.
In addition to that, I think it is really important for young people to learn that no region of the country has a monopoly on moral behavior.
The state history taught in the schools in the states covered by the Northwest Ordinance of 1787 (including part of Minnesota, though not DeSmet, I think) tends to be heavy on pride in the fact that slavery was outlawed in these states (as if one could inherit moral virtue just by living in a place).
The history of the dispossession of Native Americans in the region is rather sketchier. My recollection is that Ohio History as taught in my school covered topics related to Native Americans something like this: Mound builders, Simon Kenton leaps off a cliff, massacre of Christian Native Americans at Gnadenhutten, Newcomer and Newcomerstown, River Raisin, then the Native Americans inexplicably disappear from the region and its history.
Better coverage of the problems associated with seizure of lands by the settlers coming into Native American regions is all to the good. Context is needed of course, but the Little House books provide a regional entree to the topic that may otherwise be missing.
In a similar vein, I did not think that anyone in the state of New York could have owned slaves, but this is not true historically.