After Nellie Oleson and Percival Dalton get married, they end up having a baby in the episode Come, Let Us Reason Together.
In true Nellie Olsen fashion, they are surprised to learn that she has twin babies. She has a boy and a girl, which they name Benjamin and Jennifer.
The fact that Nellie and Percival have twins is rather fitting because they were having arguments about whether to raise their children as Jewish or as Christian. Percival’s father strongly objected to their children not being raised Jewish when he came to visit Walnut Grove.
At the end of the episode Come, Let Us Reason Together, because Nellie gives birth to twins, so they compromise on the issue and decide to raise their son as Jewish and raise their daughter Jennifer as Christian, which is a decision everyone is happy with.