The Parent class has the following constants that seems to be erroneously not declared static (and if they should not be, then a comment explaining why would be good).

    private final int LEFT_INVALID = 1;
    private final int TOP_INVALID = 1 << 1;
    private final int NEAR_INVALID = 1 << 2;
    private final int RIGHT_INVALID = 1 << 3;
    private final int BOTTOM_INVALID = 1 << 4;
    private final int FAR_INVALID = 1 << 5;

These now consume space in every Parent instance, which is often the bulk of all nodes used in a scene graph.