I think your idea of placing beauty products in the girls changing room is fantastic and very thoughtful. I would fill brightly colored plastic containers with products of all kinds. For hair products, try Paul Mitchell. It is great for all ages and the chic white and black bottles would look cool in a bright pink container. Mac makeup is perfect too! Some cosmetics companies will send out a makeup artist if you purchase enough products so be sure to ask. It would be fun for the girls to have a pro there to help them with their hair and face. You should also put Polaroid or disposable cameras in the dressing room so that they can document their new looks.
Why not cover the tables in brightly colored beach towels instead of tablecloths. Fill inexpensive glass vases with colored sand by Crayola Play Sand from Walmart (see some of my earlier postings) and flowers or sparklers that they can play with and light after the sun goes down. I love these beach ball plates too...disposable!