Get some colored paper or let your child color some regular white paper. Cut the paper into strips of similar width and length. Glue together the ends of one strip to make a ring. Insert the next strip of paper into first ring and glue together the ends of the second strip.
Repeat this step as many times as necessary to reach the desired length of the garland.
You can make several different garlands by changing the width and length of the paper strips or by combining strips of two (or more) different lengths in a single garland.