Our 5 year old daughter wanted to be a robot for Halloween, so we went to work on her robot costume. Salvaged some left over foam-core board and cut it to a size to fit her. Purchased some dryer venting, battery operated flashing lights at the local thrift store ($20, yeah I could not resist), and some metal spray paint.
Printed out gauges and reflectors from online and put it all together. Our daughter helped by cutting out the pictures and choosing where to place them, and with the original ideas for what a robot should look like.
Used duct tape and a glue gun to put things together. Added pieces of used foam rubber inside for comfort in wearing the costume (mainly on the shoulder area). The feet were just more foam-core board sized to fit over shoes. The body "hinges" with duct tape to allow her to get into the costume. I put a bolt with a wing nut to hold it in place once she is in it. The dryer vent legs and robot shoes are taped together, and we safety pinned the top of the dryer vent to her pants to keep them up. All edges were duct taped for strength and to keep any sharp edges away from our little one.
Used the bottom half of a orange plastic pumpkin to make the lens cover for the helmet top light. A foam pad with a circle cut out in the middle gives comfort to the head piece and helps it stay in place on her head. The lights on the body have a switch on the back to cycle them on and off as you want.
End result: She loves it and we have received good feedback from those that have seen her in it!