How should authors choose subjects for biographies for children?

Biographer Elizabeth Partridge has argued for longer biographies for older children and young adults. Children can find biographies about people such as Adolf Hitler, Benedict Arnold, Fidel Castro, Ho Chi Minh, and Lenin. What are the limitations of books about figures such as these that are written for children. Do the limitations of vocabulary and page length found in juvenile literature allow adequate treatment of controversial subjects? Even picture book biographies deal with figures that are less than perfect and humanly flawed. What information do authors owe their child audiences? How would you go about choosing a biographical subject if you were to plan a book for children?