Check out some of these ideas - most of which can be made with things you have around the house or can buy CHEAP! By the way, these costume ideas will work for adults, too!
Cow - Take a white sweat suit and draw black splotches on it in indelible ink; color them in. Make udders out of piece of pink fabric: Cut two BIG udder-like shapes, sew them together and stuff with poly-fill, attach to the tummy of the sweatshirt. Make a tail out of white fabric and stuff or wire for shape, glue a little black yarn at the tip of the tail for fringe, attach to the seat of the sweatpants. If you can't find a ready-made cow nose, brown out your child's nose and mouth area. Take an old headband and attach cow ears made out of fabric: cut two large triangles of white fabric, sew them together and stuff, attach to the headband and glue a little black yarn on the top of headband for "bangs". My daughter did this three years ago and, with a little sign around her neck that said, "Got Milk?", she won the costume prize in our neighborhood.
Static Cling - Take a black sweat suit and pin socks, a little towel, a dryer sheet, etc. to it. Mousse and spray your hair to stand on end.
Skeleton - Dress your child in a black sweat suit, paint "bones" using glow-in-the-dark fabric paint. Finish with scary make-up and a top hat.
Hobo - Use a pair of Dad's old pants or overalls, a beat up hat and a flannel shirt. The key words here are old and beat up! Use an eyeliner pencil (black or brown) to shade in some beard "stubble". If you like, you can stuff the shirt with wadded up newspaper to make a big belly.
Hippie - Torn up jeans (all kids have 'em), a a tie-dyed T-shirt or an old rock band concert shirt (Grateful Dead?), and some sneakers. Tie a bandanna around the kid's head and finish off with a pair of wire sunglasses and some love beads.
Ghost - Everyone has an old white sheet, right? If you don't, get one cheap at the Wal-Mart (about $4). Color two large round eyeholes with a permanent black marker, then cut out the middle to make spooky black-rimmed eyes. Get creative and add a hat and make a mouth using black permanent marker or felt.
Bunch of Grapes - Blow up small round purple or green balloons to about 6" in diameter. Dress your child in the same color pants and shirt (if you can match the color of the balloons, that's perfect - if not use black or brown). Use safety pins to attach the balloons to the child's clothing.
Junk Drawer - This one's easy! All you do is dress your child in all one color and attach items from your junk drawer to the clothing. Pencils, a tape dispenser, drawings, ribbon spools - whatever you have!
Zorro - Black pants and black collar shirt, with a red scarf tied around the waist. Add a black felt hat, black eye mask and black cape.
Greaser - White T-shirt with the sleeves rolled up, rolled up jeans and sneakers or penny loafers. Slick the child's hair back in a "ducktail" with styling gel. If you have a red windbreaker, he becomes James Dean. A black jacket makes him the Fonz.
Scarecrow - Old jeans and shirt with patches sewn on and tie colored yarn around the bottom of the pant legs and the shirt cuffs. Add an old straw hat and some hay bits sticking out of the cuffs and pantlegs.
Mr. Potato Head - Cut a hole in the bottom of a large burlap bag so it will fit over your child's head. Cut armholes in the appropriate place on the sides. Attach elastic to the bottom so it will be snug around your child's hips but they can still get into it. Make eyes, nose, moustache and mouth out of felt and glue onto the front of the bag. Have your child put on the costume, then stuff him with crumpled newspaper.
Pumpkin - Same as Mr. Potato Head, only use a large orange bag (you can also use orange fabric, folded in half and sewn down the two longer sides). Paint the child's face and neck green for a stem with watercolors or face paint.
Post-It Note - Cut a large piece of cardboard into a square big enough to cover the front of your child. Cut several pieces of posterboard in the same size square and glue them together along the top edge. Attach the cardboard square to the yellow posterboard squares using string and a hole punch (this will fit over your child's head, using the string as a shoulder harness). Write a note on the top note with black magic marker.
Mime - Black long-sleeved shirt and black pants. Paint the child's face white with commercial skin paint. Add black triangles over eyes for expression and red lips with a large cupid's bow. A red beret makes it more authentic.
Slice of Pizza - Get a large piece of 1/2" thick, two foot wide foam about twice the length of your child. Roll up about 10" from one of the narrow ends and hot glue it to make the crust. Fold the foam in half width-wise and cut both layers into a triangle, from the "crust" to the top. Glue along the sides to the tip to seal edges. Cut a large hole in the front slice (the one with the crust) for your child's face and two large holes in the back slice for his arms. Paint the back of the slice and the crust light brown and the front of the slice red for sauce. Sponge paint white "cheese" onto the "sauce" and brown on the "crust". Cut toppings (pepperoni, mushroom, black olive, green pepper) out of construction paper and glue onto "sauce".
Reposted from http://somd.com/holidays/halloween/costume.htm: Southern Maryland Online
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