Sarah, Plain and Tall, by Patricia MacLaughlan, 1985

Caleb can't remember his Mama, who died the day after he was born, but Anna will never forget her singing voice on prairie evenings. To Anna's surprise, Papa advertises for a new wife, and Sarah Wheaton from Maine writes back. She visits to decide if she'll stay, bringing yellow bonnet, seashells, and a cat. A tender romance unfolds between Sarah, Papa, and the children who desperately hope Sarah will stay, despite the lure of the gray-green sea. A charming story, remarkably short for all its tale and texture, its characters warm and memorable. Strongly recommended.