Project Gutenberg has a wealth of free downloads available.
Books in English in the Children's Fiction section include:
The Railway Children by E. Nesbit
Ragged Dick, Or, Street Life in New York with the Boot-Blacks by Horatio Alger Jr.
The Coral Island: A Tale of the Pacific Ocean by R. M. Ballantyne
Beric the Briton : a Story of the Roman Invasion by G. A. Henty
The Phoenix and the Carpet by E. Nesbit
Adrift in New York: Tom and Florence Braving the World by Jr. Horatio Alger
The Coral Island by R. M. Ballantyne
The Boy Knight: A Tale of the Crusades by G. A. Henty
The Magic Pudding by Norman Lindsay
The Luckiest Girl in the School by Angela Brazil
Friends, though divided: A Tale of the Civil War by G. A. Henty
The Princess of the School by Angela Brazil
The Treasure of the Incas: A Story of Adventure in Peru by G. A. Henty
UNITED WORLD MOVEMENT FOR CHILDREN (UWMC)