I don't understand what do you mean by 'adult music'? They don't listen to children songs anymore, but Beyonce? Or some songs which are vulgar or unappropriate for kids with words which are not for kids?
Either way, you can't prevent them from listening to it. And I don't think you should. Maybe it's just a phase, after that, they maybe start listening to Mozzart, after that it will be rock, pop, blues, I don't know.
However, your job there is not to choose which genre of music your children will listen to, but to explain to them why is that the way it is. Why there are bad words, songs with bad words, how the bad words make other people feel and so on. You need to help your children to get the best of their personality and become good people.
That way, they will listen to that kind of music, but they won't use that kind of words in their lives, if we're talking about cursing and unappropriate words.
After all, music is art, it's the way musicians express their feelings and visions of love, life, fantasy, lessons, but also anger, rage, and everything else possible or impossible in this life.
There is always both good and bad, but bad words in a song won't make people feel bad, because those are just for rhyme and singing, while if you say bad words to someone in real life you can hurt them, and make them feel bad, or sad. Teach them that. Good luck.