Gladys, this story does not say that the girl was 13 or 10. It does say that the boy is 15. Not a 15-year-old man, but a boy. There is a big difference if the girl is 13 or 10. There is a difference if they were making out, as children will do. The truth is that pubescent children experiment with sexual behaviors. This is the very reason that sex ed should be taught in schools, that parents should tell their kids something other than "don't you dare!" and that parents need to recognize that sex is happening. 
That said, if the boy cornered the girl and forced her into sex, that's a whole different scenario and criminal charges may be appropriate.