Will anyone find out about it? IPhone?

So my older cousin stole my iPhone and downloaded adult thing to it she opened all of them once and then deleted them My iPhone is jot connected to any other device by iCloud will anyone see this or find out about it?

Why don't you tell on your cousin for doing this? If not, I understand. You can reset your iPhone and restore to an earlier time with iTunes and you may want to tell Apple about this @ www.apple.com good luck

Nope you'll be fine if it's in the web browser delete history and cookies and if in an iTunes account was used just delete the iTunes history.