If my big guy is still into Stormtroopers in a few years, we may need to do this.Kids Stormtrooper costumes made from crafting foam. Search for kid's stormtrooper costume on Instructables dot com.
This is my cheap attempt at stormtrooper costumes for my 4 and 6 year olds. It's made to be lightweight and flexible for comfort but still hold true to the movie.
Mainly because I can never keep them straight, Star Wars costume evolution stormtroopers infographic.
Picture of Star Wars Scout Trooper Más