Hi, Brenda! The Flag Retreat Ceremony at the Magic Kingdom is a tear jerker for me! I get misty eyed every time I see it!
The ceremony is performed at 5:00 o'clock each day, and you do not have to be a veteran to participate - although any time that I have seen the ceremony, it has been a veteran in the honored position. The guest chosen to participate has to register on the day you visit the Magic Kingdom at City Hall. It is typically done on a first come, first served basis, so you'll need to go to guest services as soon as you arrive in the theme park.
The participant has their photo taken, and they have always in the past been given a commemorative pin. It is a beautiful ceremony, even if you are not participating, so try to make sure your Boy Scout gets to see this wonderful ceremony!
Have a magical vacation at Walt Disney World!