opening a child window

[Andy Gilman <amgilman myfairpoint net>]

I seem to be a perpetual newbie and I suspect that there is a pretty
straightforward answer to my question, but so far it has eluded me.  I
have written a small program for my own use that begins with an opening
window and then opens child windows as needed (e.g. to add data, or to
show the data sorted in a particular way).  Using Gtk::Main::run, this
is no problem.  I simply create an instance of the window I want to
call and then "run" it.  But I see that Gtk::Main has been deprecated
and Gtk::Application is preferred.  I can call the initial window with
this, but cannot figure out how to call the child windows.  Any help
would be greatly appreciated.

Andy