Hi Sebastian,
I think that the main issue with crossing state lines with an unrelated minor has to do with illegal activity. If someone is already doing something illegal with the child, by crossing the state line, the punishment may be much greater than if they stayed within one state.
I believe that it is pretty common for family's to bring along their child's friend on a vacation. So I do not think that you and your brother traveling with a family friend should be a problem. But just to be on the safe side, I suggest having your parents provide a written letter of approval to show that your friend has their permission.
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(¸. Michelle ¸.·´
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