sub-pages into one page

[Timbow]

I want to make a theme for a site which will have complex long page layouts, as is the fashion. so a page might have a full width banner and title then some full-width text then three columns of something punchy, then an article with a sidebar, etc. etc.. I thought I would achieve this in a flexible way by making main pages which contain their own child pages. Each child page would use a template - full width, 3 columns, left sidebar, whatever and I would build up the parent page like that. I have made a sketch, below.
   

So what would go in my template.php?

First the header with the menu of parent pages, then

get first child page content
get second child page content (if it exists)
get third child page content(if it exists).. and so on

Then the footer.

But what would the actual php code need to be? I don't think I would need page titles. I don't think I would need any child-menu or i18n plugin either. The parent pages wouldn't have any content of their own. I wouldn't need anchors down the page like a one-page site.

Not a feature request, but I need some help with rudimentary php. Is it as simple as I think?