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Spending the night without any sexual activity is not per se illegal if the parents consent. If, however, you are implying sexual activity of any kind (even just fondling) this age difference is illegal in every state I know about and federally. If a state line was crossed to get to the child, it can be a federal crime.
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Here is an excellent article explaining the age of consent in Louisiana. http://www.legalmatch.com/law-library/article/louisiana-age-of-consent-lawyers.html