Evil is symbolized by a big balloon that is flown by a girl too small and helpless compared with him (helplessness expressed by girl´s white hair, childlike by a detail that the girl has only one shoe and one white sock). Similarly to evil, the power of balloon is hidden and initially not well seen at the first sight, the power of the balloon grows with the freedom provided, little girl is too far away and plays carelessly, without realizing that her balloon will carry her away.
Similarly to the true life, evil is hidden in something (balloon in this case) where we would not expect it at all.