I like it, but I have some ideas about the timeline choices.
I was talking to co-workers who love the books and historical clothing and went on this mini tangent about my thoughts about the show and the discourse about bonnets, timeline, etc.
The main thing I think they are doing is blending/shifting the timeline to make it shorter/streamlined. With the girls older, it allows greater narrative control.
That said, knowing it's supposed to be 1869 in the show, it clearly is not.
1869 would still have a good number of hoop skirts. Even out in the Prairies, those town women would have travelled with their hoops and worn them. But we never see any.
This was the first clue that made me think they are shifting the years. Despite saying the Civil War ended three years ago. ( which still doesn't make sense, as 1869 is four years after the end.)
Caroline's dresses are much more a-line and slim-skirted. They are much more natural form than the hoops of the Civil War.
The clothing it self is more representive of the mid early to mid 1870's. Fashion itself is an interesting thing because style and silhouette always tend to follow the same look across economic classes. It's the fabric and trimmings that make the classes stand out. Time may move more slowly across the prairies, but fashion always follows.
Costumes aside.
If they are blending years, time shifting. It makes sense to make the girls older. It's harder to have a 3-year-old narrate the show. But the main thing I take away from it is that condensing, moving the years later, works because the books often have years in them.
They can spend a season on a book, exploring the themes while Laura is still youngish-looking, and by the time they get to Shoes of Silver Lake, Hard Winter, etc.
She will be the age of Laura in Little Town on the Prairie.
Mary will be the right age for college.
They won't have to recast if they want to continue the whole series.
Anyway, that is my theory about the show.