My four year old son is fascinated by lighthouses, so much so that our trips usually revolve around stopping by a lighthouse. He wanted to be the Chincoteague, Virginia, lighthouse this year so this is what I came up with. I used a photo of the lighthouse for inspiration.
The body of the lighthouse is an adult size XL sweatshirt. I cut off the sleeves, then hot glued two strips (width 5 1/2 inches) of white polar fleece to the sweatshirt along both edges of the fleece. The top strip is cut by the arm holes and is not a complete round. Then, using colored squares of felt, I cut out windows freehand and hot glued them in place. I snipped a small hole in the back of the collar and fed a drawstring through so that the neck could be tightened for trick-or-treating. A pool noodle was cut into a 38 inch length and then duct-taped into a circle. This goes over his head, but under the costume, to give a circular effect to the lighthouse. A large metal ring that I found at a garage sale is placed in the bottom band of the sweatshirt to maintain the roundness.
The light (hat) was trickier. I used an old Zorro hat from a dress up costume because it has a string that can keep the hat in place when my son moves his head. First, I hot glued a 1-inch wide felt band along the hat. Then I hot glued eight Popsicle sticks evenly around the hat, sticking up from inside the felt band. I used a scrap of muslin draped and glued inside the sticks. I placed a touch light (the kind for cabinets or kitchen drawers) on the top of the hat. When gluing the muslin I made sure to overlap the seams (about an inch) in the back so that I could stick my finger in to turn on/off the light. I cut a round of cardboard the same size as the top of the hat and covered it on both sides with black felt. This was attached to the Popsicle sticks with hot glue, gluing some of the muslin at the same time.