Gtk::TreeModel::ColumnsRecord's children

[Sergio Perticone <g4ll0ws gmail com>]

I've this classes:

class Window : public Gtk::Window {
   // ...

protected:
     class ModelColumns : public Gtk::TreeModel::ColumnRecord {
         // ...
     };


     ModelColumns columns;
};

How I can have access to the children?
I've tried columns.children() but g++ says:
error: ‘class Htc::Window::ModelColumns’ has no member named ‘children’

Thanks,

s.