She resumed writing short stories, which began to appear in newspapers and then magazines starting in 1910. Charles took on a lifelong role as Kathleen's literary agent, and also took care of many household management roles as she became increasingly successful as a writer. Shortly after becoming a new mother, she wrote her first novel, "Mother". It started as a short story in "The American Magazine" in 1911. A publisher asked her to expand it into a novelette, which became a national sensation and earned the praise of Theodore Roosevelt for its celebration of large families. A devout Catholic, she wrote the book in part as a commentary against birth control, which was rapidly influencing women's attitudes about motherhood. Her 1914 novel "Saturday's Child" received a positive, lengthy review from William Dean Howells, who remarked on her sensitivity to class issues.