Sexual imagery
As the children progress in their rouse, the intimacy of their situation, and the desperation of their attempt to fill their parents' roles in the home cause the siblings to develop incestuous desires. The novel is full of erotic imagery, ultimately culminating in an intimate scene between them when they get naked together, and then are discovered engaging in incest.
Images of death
The most gruesome of the imagery in the book is the imagery of the dead body of the mother, brought into the cellar, covered in cement, and then decaying, emitting an ungodly smell into the entire home. The children literally live in the stench of their own mother's death. This is not the only instance of death imagery at all, but it is the primary image.
Home imagery
Most of the story happens in the home, trapped in the ghost house of the life the family used to have. The children try constantly to take solace in the home, playing house to try and find some way of surviving. Perhaps this imagery represents the children's desperate desire for things to be the way they used to be.
Imagery of the immature
The youngest of the children still sleeps in a crib-like bed, but he's six. Jack and Julie are described as poor representations of what the parents did so well. Even their attempt at a burial in cement is badly done, a depiction of the complete immaturity of these children.
