So far all we have to go by is the trailer from the Square-Enix page. Here is the dialogue from the trailer, if you’re running on a slow machine or connection.
Narrator: The planet weaves a cruel fate for men. Children are always the first to suffer. Geostigma, Jenova, Reunion. Children who have lost hope, respite for the soul. And so he takes sword in hand, once again. Final Fantasy VII – Advent Children.