Whats happens if you have underage s*x?

Question

Ive always wonder what they would actually do to people, of the same age, having under age s*x, because technically there breaking the law lol but as far as im aware nothing happens.

Answer 1

 but what happens if the girl is older for days and they are both 15

Answer 2

nohing happens really ulsess its real serious like a 18 year old boy has s*x with a therteen year old girl ? :L

Answer 3

nothing, tons of underage people have s*x and the law knows that, wether they want to admit to it or not.