Ask your preschoolers what they already know about the differences between night and day. Have them tell you about activities that take place during the day and what happens at nighttime. Write their responses down on paper and have them illustrate their thoughts. You can also take paper plates and have them paint them yellow to represent the sun. Cut triangles out of construction paper and help your preschoolers glue them around the outside to make the sun's rays. To illustrate night, cut stars out of construction paper and help your preschoolers apply drops of glue. Sprinkle glitter onto the stars and lightly shake off any excess. Allow the stars to dry completely.
Show your preschoolers how plants and flowers grow differently during night and day. Fill two paper cups with soil and then plant grass seeds in them. Have the preschoolers water the cups then place one in front of a bright, sunny window. Put the other cup in a dark area of the room or a closet. Every morning, have the children check and record the progress of both cups. Talk about how the sun helps plants and flowers grow.
Choose a book about animals that are active during the night, particularly raccoons, owls or bats. Print out pictures of both nocturnal animals and animals that are active during the day. Place Velcro on the back of each picture and create a chart based on nocturnal and diurnal animals. Ask your children to place each picture in the corresponding column based on the time of day when the animals are awake.
Take pieces of white construction paper and instruct your preschoolers to draw stars with white crayons. You may have to help them press hard with the crayons. Mix a black or dark blue watercolor paint to illustrate nighttime and have them paint over the stars. The paint will not adhere to the crayon wax and the stars will magically appear on the paper. Take this opportunity to discuss how the sky looks during the day and at night.