On our recent, 12/11, cruise, I found out that the salon does offer some special services for younger cruiser (8 and above, I recall) during certain hours, 8 or 9 pm after the regular spa hours. One was called Little Princess and offered a couple choices from a mini facial, pedicure, manicure, hair styling. There was also a Mommy and Me service. I originally booked the Little Princess for my 10 y/o dd, but unforunately later had to cancel it. I think the price would have been around $60.
Sharon, the stylist who did my hair for formal night, told me that there are several ladies that work in the spa that love to work with the girls.
Hope this helps and enjoy your cruise!