1. @override
SimpleNode onLoadChild(String name, Map data, SimpleNodeProvider provider)

Callback to override how a child of this node is loaded. If this method returns null, the default strategy is used.

Source 

@override
SimpleNode onLoadChild(String name, Map data, SimpleNodeProvider provider) {
  if (onLoadChildCallback != null) {
    return onLoadChildCallback(name, data, provider);
  } else {
    return super.onLoadChild(name, data, provider);
  }
}