Cut tulle strips. Cut the tulle twice as long as you want the finished length of the tutu to be. Strips should be about 1.5 inches to 2 inches wide. Cut the entire piece into strips.
Cut waistband. Using elastic for the most versatile and easiest fit, cut a piece to fit the waist of your child, plus 1 inch. To use a ribbon for the waistband, measure the length of your child's waist. Add 12 inches on each side (24 inches total) to allow room to tie the ribbon after the tutu is completed. Cut the ribbon. With chalk, mark 12 inches in from each end so you know where to stop attaching the tulle.
Attach tulle strips. Fold one strip in half. If you are using elastic, begin 3/4 inch from one end. If you are using ribbon, begin at one of the chalk marks. Slide the folded end of the tulle under the waistband material. Take the two ends of the tulle strip and place them through the loop formed by the folded end of the tulle and the waistband. Pull it tight. You will now have a "raven's head knot" securing your tulle to the waistband. Continue with remaining tulle, placing each strip very close to the previous one. Alternate colors as desired.
After all the tulle strips are added, overlap elastic ends 1/2 inch. Stitch securely by going back and forth repeatedly.
Lay out the pattern. You can buy a jazz pants pattern or you can use any pull-on pants pattern, such as pajama pants. Alternatively, use a seam ripper and remove the seams from a pair of pajama pants that your child owns that fit tightly. Lay the pieces out on the black fabric you are using for jazz pants. Add an extra 2 inches to the top of each piece.
Sew the leg seams. Pinning the wrong sides together, sew the long, outside leg seams and the inner leg seams of the pants. Some patterns or pajama pants have no outside leg seams -- only inner seams. If this is the case for you, sew only the inner leg seam. Keep pant legs inside out.
Sew the crotch seam. Place right sides together and pin along the crotch seam. Stitch, reinforcing the ends of the seam. Iron the seam open.
Form waistband. Iron the top of the pants under 1/4 inch. Then fold the top of the pants under 1 inch. Iron, and then stitch along the folded under 1/4 inch portion of the fabric. Leave a 1-inch area unstitched.
Insert elastic. Cut a piece of elastic the length of the waist of your child. Add 1 inch. Using a large safety pin attached to one end of the elastic, thread the elastic through the waistband opening, bunching the fabric as necessary. Stitch elastic together, overlapping ends 1/2 inch. Stitch opening closed.