I hate to rain on your parade, but due to rising security risks they no longer accept mail to "any recovering soldier". I got an email earlier this week at work asking you to do this, when I researched for more info I found out that they've stopped it. 
Holiday Cards to Wounded and Recovering Soldiers
Walter Reed Army Medical Center
Holiday Cards to Wounded and Recovering Soldiers
Walter Reed Army Medical Center officials want to remind those individuals who want to show their appreciation through mail to include packages, letters, and holiday cards addressed to 'Any Wounded Soldier' or 'A Recovering American Soldier' that Walter Reed cannot accept these packages in support of the decision by then Deputy Undersecretary of Defense for Transportation Policy in 2001. This decision was made to ensure the safety and well being of patients and staff at medical centers throughout the Department of Defense.
In addition, the U.S. Postal Service is no longer accepting "Any Service Member" or "A Recovering American Soldier" letters or packages. Mail to "Any Service Member" that is deposited into a collection box will not be delivered.
Instead of sending an “Any Wounded Soldier†letter or package to Walter Reed, please consider making a donation to one of the more than 300 nonprofit organizations dedicated to helping our troops and their families listed on the "America Supports You" website.