Star Wars: 20 Things You Didn't Know About The Empire Strikes Back
12. Children Were Hired To Play Rebel Extras
Irvin Kershner made use of one of the oldest tricks in the book to accentuate the scale of the Rebel hangar set, by hiring children to play Rebel soldiers to appear in the background of wider shots.
Their short stature would suggest the hangar was actually larger than it really was, and if you want to be totally cynical about it, it probably meant they didn't have to pay their extras as much.
Still, it's basically impossible to tell when looking at these scenes in the movie, so bravo.