Use one of the boxes to be the main part of the train (the green part in the picture below). Tape one end shut and cut the flaps off the other end (save the flaps to use for some of the details!). Cut away half of the side of of the end you tapes shut. This will be the top, where you attach the window part of the costume (the red part in the picture below). Make sure your body can fit through the opening.

Use the 2nd box for the window section of the costume (the red part in the picture below). Cut the cardboard until it is the desired shape and size and then tape it on the 1st box. It should have 3 windows, the back side can be solid. The top half of your body will be in this section, the roof resting on your head.

Use 4 paper plates on each side of the train to be the wheels. Use a scrap piece of cardboard to make the connector as shown in the picture below. Use the extra catrdboard to make all the other details of the train such as the smokestack and the front grill section. Use tape to attach everything together.

Once your train is constructed, paint it as desired.

Don't forget to wear an engineer hat, overalls, and even a bandana loosly tied around the neck.

NOTE: If you do not want it so the costume rests on your head, add shoulder straps inside the window section using thick elastic or rope.