Translation:The girl is in the front, and the boy is in the back.
Not really. Behind mostly makes a comparison between two things, meaning 'mögött, után'. 'Hátul' stands in itself. What is behind something/valami mögött van, than it probably also means 'hátul van'.
On a second thought, I've realized that 'behind' can be used alone, but in the meaning of left behind, fall behind. I wouldn't translate it as 'hátul' either, because 'hátul' is a stable place, while behind is a bit vague. If someone is behind me in a line, I'd say:
Hátul van - He's at the back; when he is among the last ones in the line.
Hátrébb van - He's behind; he's somewhere in the line, I don't know where, but I'm ahead of him.