I was going to say that maybe requiring authorization from the parent might be the way to go, but apparently that is already the law in CA.
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In California, there is the Filante Tanning Facility Act of 1988.
The law requires anyone between 14 and 18 to bring a note from his or her parent in order to get a tan. Parents are required to accompany any child under 14 who wants to use a tanning booth.