Sure, you can buy decorations for literally any holiday you can think of. Halloween cut-outs, Thanksgiving pumpkins, and Christmas ornaments abound. You can go to any online store or party supply shop, pick out a few favorites, and call it a day, but is that really how you want to do it?
Do you want to spend tons of money on cheap cardboard and banners that probably won't make it through the holidays? It's so much more fun to actually create your own holiday decorations; it can be much less expensive, children will enjoy helping (thus creating some terrific project ideas), and it will mean more in the long run. You'll feel more like keeping your creations for next year, too.
Different holidays will require different craft supplies. For instance, you may want glitter and glitz for New Year's, green construction paper for St. Patrick's Day, and fake "snow" for winter holidays. How many supplies you stock up on depends on how far you want to go. If you just want simple cut-outs like pictures printed from the Internet and then colored, it won't cost you a penny; if you're planning to make hugely decorative banners with glitter, paint, ribbons, and other odds and ends, it will put a little more of a dent in your pocket.
Christmas. For Christmas you can either make tree ornaments (homemade clay nativity figures fastened to the tree with ribbons, foam cut-outs decorated with glitter, easy wooden picture frames with the photo of your choice, and many other possibilities) or things to sit around or hang. As mentioned before, you can print out coloring pages or other pictures and have kids fill in the colors; you'll probably want to ask older children to do this to make sure they can stay inside the lines.
For simple decorations to scatter throughout the house, you can either "hire" a friend or family member who is good with his or her hands to make some woodwork pieces, or you can get creative by getting Christmas craft project idea books and choosing which items you want to make. I once made a tiny Baby Jesus figure by hollowing out a walnut shell, gluing cotton inside to make swaddling clothes, and finishing it with a wooden bead and a painted face to make Jesus' head.
Hanukkah. You can make homemade dreidels for this Jewish holiday; find instructions that tell you how to fasten paper to form a cube, then write on the appropriate Hebrew letters. I once tried to make a dreidel in which a pencil was stuck through the bottom to make it spin. You can make your own chocolate coins (called "gelt") for the popular dreidel game.
Easter or Passover. Most children have delighted in coloring Easter eggs, but you can make egg decorations too. Stock up on construction paper or regular paper (you can get very thin paper or thicker paper like the kind found in drawing tablets) and cut out a bunch of egg shapes. Give kids markers, colored pencils, or glitter pens, and set them loose.
The best eggs can be chosen to decorate. When I did this as a child, I would scatter my "eggs" throughout the living room, inside my Easter basket, around the table, and anywhere else I could hide one. You could also glue these eggs onto an "Easter wreath" or make them part of another, bigger project.
If you celebrate Passover, you could ask children to "illustrate" parts of the Passover story on plain drawing paper, and then make the drawings into a type of mural or hanging decoration. Dress up clothespin figures as Moses, the Hebrews, or even Pharaoh. This is very simple; take a clothespin, glue on plain white, brown, black, or other solid-color pieces of material and then cotton for beards and hair. Eyes, noses, ears, and mouths can be drawn on the "face" of the homemade doll.
Thanksgiving. Pumpkins aren't just for Halloween; they are also associated with fall and can make great Thanksgiving decor. Instead of the traditional carving, ask kids to get creative and decorate pumpkins in new, unique ways. Glue a yarn wig on the pumpkin's head; draw on a face with glitter pens. "Dress" the pumpkin up by winding a bright piece of material around the bottom. If the kids hate "pumpkin guts" (as I always did when I was younger) then these are great alternatives to the traditional carving.
Cut out and color leaves to scatter here and there. You can either self-decorate leaves, or use orange, red, green, and yellow construction paper and simply cut out the leaf shapes. For more advanced children, the clothespin technique mentioned for Passover can be used here; just use dark material for Pilgrim dresses and capes and buckskin-colored material (preferably a leathery material) for Native Americans.
Halloween. Halloween is a fun holiday to decorate for because of all the possibilities. Kids can cut out witches, goblins, vampires, pumpkins, black cats, and all sorts of things. Construction paper will again come in handy here, but you can also make scary figures out of clay or dough. Even dressing a favorite doll as a witch with a homemade broom and displaying it prominently can be a cute homemade decoration.
If you'd rather do something more craft-oriented, you can make a Halloween wreath (orange and black instead of red and green, with little miniature gourds, clothespin people, construction paper cut-outs, and anything else you can think of) or autumn-related items like wooden scarecrows (something like this could also be made with wood, clothespins, popsicle sticks, etc.)
By Lacie R. Schaeffer