The Big Bed is a recurring item in the Harvest Moon and Story of Seasons series. In many Harvest Moon games it is required for Marriage, and is a piece of furniture for purchase. The item generally has two different expansions for the size of your bed, each adding another space for another person. The first upgrade makes it a double bed so you can get married, the second upgrade makes it a triple bed so you can have a child.
The Harvest Moon Wiki