During the episode May We Make Them Proud, Adam Jr, the son of Adam Kendall and Mary Ingalls Kendall, died in a fire at the school for the blind. Mary went into shock after the death of her son.
Later on the television show, Mary and Adam moved to New York after Adam regained his sight and began practicing law. But they never had another child on the show, and Mary and Adam last appeared on the show in the Christmas episode A Christmas They Never Forgot.
In real life, the real Mary Ingalls never married nor had any children.