Towards the end of the episode, Mr. Simms tells Charles that he and his wife were married in the Walnut Grove church. But previously, men in town, no older than 40 themselves, said that they built that church with their own hands. Both statements can't be true.
The tornado at the beginning would have surely been heard by a family member inside the house well before Charles discovering it by opening the front door.
The duration of the tornado is much longer than it would have been in reality. It would have swept by the Ingalls farm within minutes...not hours as depicted by their emerging from their shelter in the bright light of day.
Towards the end Charles and Caroline hug after they decide to stay in Walnut Grove. Caroline's wedding ring is seen on her left hand, but Charles' is missing. That would not be in the late 1800's.
During the opening credits, just before the doors to the barn are blown open by the wind, a person can be seen walking towards the horse.