Belles on Their Toes is a 1950 book written by Frank Bunker Gilbreth, Jr. and Ernestine Gilbreth Carey. This book was the follow-up to the 1948 book Cheaper by the Dozen which covered the period before Frank Gilbreth Sr died. Belles on Their Toes was written about the family after the death of Frank Bunker Gilbreth, and how they survived. This book is also the first time where the absence of the second oldest child, Mary Gilbreth, is explained; she died of diphtheria in 1912 at age six.