Underage actors kissing?

I'm thinking about auditioning for a role in a romantic teen movie, but it's only a book now and casting will probably be around 2 years from now. since most teenagers in films are played by people above the age of one in movies that involve romance (or anything really), I was wondering if there was some law that prevents underaged and adult actors from kissing or making out on screen?it's not like they're having sex or anything, but just playing their role in the movie. is it against the law or is that just how they cast?
Underage actors kissing?
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