WOW < GREAT IDEA!
ok well if you have a small group of kids you may want to see about having a few parents with sewing skills make a few hats , they are kind of easy and i think that one of the pattern companies has a pattern . an other idea might be to have them dress in tan and dark blue , most boys have blue and tan dress pants , and collared skirts aren't that much ( and can be used again ) I hope this helps .
trish
p.s. you might want to see if you have a local WWII re-enactment group that might be able to help you with this , also . plus you might be able to get them to be part of your show .