// By default children loading is "lazy".
// Therefore for instant loading has took place,
// it is necessary to set the NotebookLoadOptions.InstantLoading flag.
NotebookLoadOptions loadOptions = new NotebookLoadOptions();
loadOptions.setInstantLoading(true);
String dataDir = Utils.getSharedDataDir(LoadingNotebookInstantly.class) + "Notebook/";
Notebook notebook = new Notebook(dataDir + "test.onetoc2", loadOptions);

// All child documents are already loaded.
for (INotebookChildNode notebookChildNode : notebook) {
	if (notebookChildNode instanceof Document) {
		// Do something with child document
	}
}