I have so many friends with little girls and was really happy to learn to make this tutu in January 2012. They can be made adjustable if you create them on ribbons. That's a good solution for itty bitty babies, and animals. For the rest of the world, elastic is the best bet.
3/4 inch non-roll elastic - fits around the waist of the wearer
40 yards of tulle - the roll kind
Sewing machine - very briefly
Velcro - only necessary if you are putting on a dog or horse or something