My son had an army birthday party when he turned 8 and it was a BLAST. We ordered plastic helmets and dog tags from Oriental Trading. For the birthday boy, we got a helmet (really a liner, but it was heavy enough!) from a local army surplus store. We put black marks on all the kids' cheeks and gave them a fake tattoo when they arrived. The person working the door took down their names and we had a grid of items they were to get and activities to do and we'd check mark it off as if they were a recruit when it was done.
We had bought white shirts ($1 each, if you have a friend who has a business and can qualify as a dealer, shirts can be quite cheap!) We dyed them army green and had their last names put on the left front pocket area by transfer (a local printing company does one page of transfers for $1.50 and then $1.00 each shirt to press them). It was important to get everyone's RSVP's so we wouldn't waste any shirts. They changed into the shirts and got their personalized dog tags. If you know someone with a label maker, you can just put their names on a clear label and stick them to the dog tags, which is what we did after finding out the dog tags were too thick for us to just imprint their names.
What made it kind of fun was that my father had some fatigues on and a shirt with his name on it and the helpers such as myself, my mother and my son's father had on the shirts as well with our names. We had our clipboards which just make it seem so official. Also the kids were referred to as "Private Smith" (or whatever their last name was) and they shouted "Yes Sir!" or "No Sir!" when asked questions. We had roll call, "processed" the recruits and then they learned how to stand at attention and then at ease, how to salute and how to march. We taught them a marching song and marched around singing it, but that might have been a little too much.
The best part of the party was the obstacle course. We already have a small jungle gym with a swinging rope. We happened to have a red plastic sled that would hold some water and the kids would have to swing over the water from the rope, drop down and then climb over a wooden wall that we built (the most costly of items because of the cost of wood). We had to dig 2 deep holes in the ground to make it secure . We put a six foot 4x4 in each hole about 1.5 feet down and nailed, sometimes flush and sometimes with gaps between, about six 4-foot 1x6 boards across with gaps for ease of climbing.) After summitting the wall, the kids either climbed back down the other side or jumped down. Have a spotter there for safety.
They then had to crawl under bright criss-crossed flagging/surveyor's tape (the kind you see tied to show boundaries, skinnier but similar to police "do not cross tape." They were supposed to crawl without touching the fairly low-to-the-ground tape maze. We just put some square .5x.5 sticks in the ground, 4 on the left, 4 in the middle and 4 on the right and then criss-crossed the tape, tying it off once satisfied with it. Once the kid made it through, they hopped up and kicked a soccer ball into a soccer net, both of which we happened to already possess although they are so common, you could probably borrow them. What made it really fun, was that the "sergeant" timed each kid's run with a stopwatch, blowing a whistle to start and at the finish and an "assistant" would write the times down all official like. They did the obstacle course again and again to beat their times or others' times and just absolutely LOVED it.
A lot of the kids went home with just a few boys who stayed to spend the night. The boys who spent the night got to play with camo colored pvc miniature-marshmallow shooters. Caution, you will find marshmallows for years to come if they play indoors. It was birthday boy and 4 others, so the shooters weren't much $. Anyway, all the kids had a great time and were pretty worn out at the end of it all. Lots of cool picture opportunities and a fairly elaborate party without major cost.
We thought about buying army tents for decoration but also for the boys to sleep in, but this was just too much and very pricey. We also thought about hanging up some camouflage netting for decoration, but the army surplus store runs out of that quick and it too is pricey. We just put up army green color streamers and a few balloons which was plenty. The cake was just a rectangle pan cake but with some plastic army men on it and a tank. We did buy a batch of plastic army men from Oriental Trading with the plan for the spend-the-nighters to hunt for them. This was too much on top of the rest of the activities, I so over plan sometimes! And don't worry about weather too much, it was totally drizzly the day of my son's party and it kind of gave it a bit of authenticity. Some of the kids got muddy, but it was exhilarating. Hope this gives you some ideas!
By Rebecca from Central Georgia