Mindless, as far as anyone can tell. A Warchild is the rotting body of a child (fetus through pre-pubescent) that floats in the air, in fetal position, surrounded by a semi-translucent spherical shell of crystallized Blood. They instinctively draw the life force from nearby creatures. It is possible to magically bind yourself to a Warchild and draw off some of the power that it draws from the living around it, and use that power. Some Blessed and Blooded mages use them as pets, guards or attack dogs, sometimes fixing them in place in their lairs to draw out the life force of invaders and kill them, or sometimes they will have the Child floating over their heads, and use them as a weapon.
Found normally, they drift over the landscape, seemingly at random, attacking any people, animals or even plants if there is nothing else available, that they happen to come near, drawing out their life energy to sustain themselves. They live essentially like a jellyfish or man o'war.
Extremely resilient, their Blood shells take a tremendous amount of force to shatter, which is the only way to destroy them. Note that when the shell shatters, it returns to liquid Blood, and could spray those around it. Touching the solid shell will not open one to corruption, but it will increase the rate at which the Warchild draws out your life. Shattering their shell and destroying them however is obviously extremely dangerous.