"Come with me or die with him," a mysterious being says to Bran and Meera as Jojen lies dying. Who is this fireball-wielding creature leading the group to safety? A Child of the Forest. The Children were the first known inhabitants of Westeros, settling long before the First Men crossed a land bridge from Essos. The ancient race has "been missing and presumed extinct," series creator D.B. Weiss explains. "It turns out that they still exist in these deep, deep northern regions where Bran and his company travel."
The Children of the Forest worshiped the gods of nature. According to legend, they were the ones who carved elaborate faces into the weirwood trees of Westeros. Bran and his party arrive at that particular tree because according to Weiss, it "lies at the heart of the world."