Why do the children follow the dog to the stream? What do they see? What happens next?

The children follow the dog to the stream after he raises a fuss after lunch. They see a bear at the river attempting to eat some of the butter that has been left in the stream to stay cold. Marguerite yells for the children to run when the dog prepares to spring at the bear. By the time the children tell the men and they go after the bear, it is gone.