Fold the paper panel in half and cut a hole out of the top, large enough for a child's head to fit through. Leave enough paper on the edges to rest on the shoulders.
At the Party:
Unfold the paper smock you have created and let party guests decorate and color their costumes.
Decorate the back of the white paper plates to look like a face. You can then tape, glue or staple the face to the front of your train costume. Alternatively, use circular construction paper cut-outs to make faces.
Write each guest's favorite number on another paper plate or cut it out of colored construction paper. Tape or staple the numbers to the back of the costume.
Once all your guests are done decorating, have them put on their costumes and form a train parade to show off their creations!