The Children see the carved faces in weirwood trees as representations of the Old Gods, if not physical manifestations of the Old Gods themselves. The Children also believe that by carving faces into the supposedly supernatural trees, they, and greenseers like Bran and the late Jojen Reed (Thomas Brodie-Sangster) , will be able to witness whatever these ageless trees observe. The weirwoods can all communicate their observations to each other, like Westerosi internet. That is why individuals who follow the Old Gods pray at the base of weirwoods and also perform important ceremonies — like their Night’s Watch vows — in front of them.