The Guardians Of The Elements

Zaire, Lilly, Alina and Aiden were all normal teens living in the ancient apocalyptic times when monsters did in fact exist.
while living in one of the only safe places (some fancy huge camp with giant walls) their lives are uneventful and boring well except for Lilly's.

While at school each of them receive a speech of some sort from an unknown entity who knows about their 'secrets'.