Decorate your classroom windows with borders. Buy pre-made cardboard borders with colorful designs and tape them around the windows. Or make your own using construction paper of different colors and stickers. Have your preschool students make the borders as a class project. Divide the class into groups, and assign a window to each group. Help the students cut out paper and draw on the borders.
Use seasonal crafts to decorate the windows. Have the students make snowflakes by folding paper into fourths and making decorative cut-outs. Tape the snowflakes directly onto the windows, allowing light to stream in through the cut-outs. Have your students make small pumpkins or witches out of construction paper in the fall and suns and flowers in the spring. Tape them onto the windows.
Buy window clings for your preschool classroom windows. Some window clings use suction cups to stick to windows. Others are made of vinyl and adhere directly to windows. Get window clings that come in the shape of numbers or letters, butterflies, school themes, animals or anything else. Affix them to your windows.
Make hangings to decorate your classroom windows. Cut out shapes of kids, animals, planets or anything else. Affix them to strings and hang them from the top of the windows. Have your students make the window hangings as a preschool art project.