Something I forgot to add is that it isn't uncommon for navel piercings to take up to a YEAR to heal.
The studio my daughter goes to has a policy where under 16s must have a parent with them, under 18s must have written consent.
My local studio says this about migration:
''There is also a specific kind of rejection, popularly called 'growing out', to which a number of piercings are prone. This is a natural process, quite often associated with a person's body growing, and is not usually accompanied by any redness, discomfort or discharge until the very late stages. This is more common in younger teenagers (who's bodies are still growing). The end result of this process, which can often take a year or more, is the loss of the piercing. We commonly see eyebrows, surface piercings and navels 'growing out' over time. There is no way of being able to tell for definite how long a piercee will keep their piercing for, as it varies so much from person to person. If you are considering a surface piercing please bear in mind the placement, as another thing that can affect the longevity of the piercing is the amount of movement that area of the body gets. The constant stretching and relaxing, of, for example, an ankle piercing, can also help a piercing to work it's way forward''