@Override
    protected void updateWorldBound() {
        super.updateWorldBound();
        // for a node, the world bound is a combination of all its children
        // bounds
        BoundingVolume resultBound = null;
        for (Spatial child : children.getArray()) {
            // child bound is assumed to be updated
            assert (child.refreshFlags & RF_BOUND) == 0;
            if (resultBound != null) {
                // merge current world bound with child world bound
                resultBound.mergeLocal(child.getWorldBound());
            } else {
                // set world bound to first non-null child world bound
                if (child.getWorldBound() != null) {
                    resultBound = child.getWorldBound().clone(this.worldBound);
                }
            }
        }
        if (resultBound == null) {
            resultBound = new BoundingBox(getWorldTranslation(), 0f, 0f, 0f);
        }
        this.worldBound = resultBound;
    }
<code>getQuantity</code> returns the number of children this node
maintains.

@return the number of children this node maintains.
jme3-core/src/main/java/com/jme3/scene/Node.java