You will need about 1/8 of a yard of fabric, two metal barrettes/ clips, and a six inch piece of soft elastic.
Step 1: Preparing the materials
Cut fabric as follows for an adult-sized hairband
1 piece: 15 x 5.5 inches
1 piece: 10 x 2.5 inches
1 piece elastic: 6 inches
2 pieces of the barrette pattern. Then snip off about 1/4 inch from the "non-pointy" end, as shown in the picture.
Cut fabric as follows for a child-sized hairband
1 piece 15 x 5.5 inches
1 piece: 8 x 2.5 inches
1 piece elastic: 4 inches
Step 2: Sewing the hairband
Repeat with the smaller hairband piece.
Step 3: Insert the elastic
The easiest way to do this is with one of those little hooks they sell for the purpose of inserting elastic, but you could also use a safety pin on one end of the elastic, and pull it through with a crochet hook.
Sew both ends of the smaller tube to secure the elastic. You can sew right across the fabric, even though it's the "right side." It will be hidden in the next step.
Step 4: Sew the hairband together
Connect the other end the same way.