Wilhelm Grimm had four children with his wife, Henriette Dorothea Wild. Their children were Jacob, Herman Friedrich, Rudolf Georg, and Barbara Auguste Luise Pauline Marie.
Wilhelm married Henriette, known as Dortchen, in 1825. She was the daughter of a pharmacist and came from the Wild family, which was closely connected with the Grimms’ circle of storytellers. The couple’s first child, Jacob, was born in April 1826 but died later that same year.
Their second child, Herman Friedrich Grimm, became a writer and art historian. Rudolf Georg and Barbara completed the family. Wilhelm’s four children were born between 1826 and 1832, during the period when he and Jacob were establishing their reputations as scholars, linguists, and collectors of traditional stories.
The number is sometimes confused with the much larger Grimm family Wilhelm came from. His father, Philipp Grimm, had nine children in total, including Jacob and Wilhelm. The question asks about Wilhelm’s own children, and the canonical answer is four.