On Google Books is the book The Theatres of Paris by Charles Hervey. on page 176 he gives a biography of Etienne Arnal who voluntarily enlisted in the "la garde du roi de Rome" in 1812 at age 14. Some months later the regiment was strengthened by youth from the orphan hospitals aged sixteen. Towards the end of 1813 the tallest and strongest were transferred to the tirailleurs.

http://books.google.com/books?id=8OQqAAAAYAAJ

See also:

page 3

http://www.aet-association.org/aet/articles/linstitution-des-enfants-de-troupe/les-pupilles-de-la-garde-imperiale/document

And this: from here: (http://www.napoleon1er.org/forum/viewtopic.php?f=7&t=23487)

G.M. La garde du Roi de Rome // Le Révue des études napoléoniennes. T. 36. Paris, 1933. P. 22-24.
- Mathieu R. Un projet de création de Garde du Roi de Rome en 1814 // Ibidem. P. 25-27.