@Override
    public boolean isChildOfParent(T_TREE_NODE node, T_TREE_NODE parentNode) {
        return getParent(node) == parentNode;
    }
Return the children of a node as a {@link List}.
<p>
Time Complexity: O(1)
<p>
Also the access to an item of the list must have time complexity O(1).
<p>
A client must not modify the returned list.

@return the children of the given node. When node is a leaf the list is
empty.
stroom-core-client-widget/src/main/java/stroom/widget/htree/client/treelayout/util/AbstractTreeForTreeLayout.java