Complex sentence: He has been put on a strict diet consisting mainly of dried prunes--but now he has the appetite of a 12 year-old! --, he must not leave the grounds except on official occasions, and he is not given any pocket money.
Split into simpler sentences: He has been put on a strict diet consisting mainly of dried prunes--but now he has the appetite of a 12 year-old! He must not leave the grounds except on official occasions, and he is not given any pocket money.