Complex sentence: The "stiyaha" or "kwi-kwiyai" were a nocturnal race that children were told not to say the names of lest the monsters hear and come to carry off a person--sometimes to be killed.
Split into simpler sentences: The "stiyaha" or "kwi-kwiyai" were a nocturnal race. Children were warned against saying the names, lest the monsters hear and come to carry off a person--sometimes to be killed.