Answer:
My response would be:
The reader learns that the ice is very thin. They know this because in the phrase "It was early winter and the ice on the lake wasn’t thick enough to support the sled and team or I would have gone across the middle." It clearly states the ice wasn't thick enough to go across the lake. This prepares the reader for what happens in the story by foreshadowing the ice cracking later on in the story.
(I don't know if the ice will crack later on in the story though)
