Forcing a child page to have a parent level permalink?

I am porting a site to WordPress and have to honour some existing published URLs.

However, I want the pages to be child pages so they appear in the appropriate menu structure.

Example:

I want to honour http://www.mysite.com/children

but I want the page and menu structure to be familylife/children.

I can edit the permalink but only the last part, so currently I cannot get the familylife bit out of the URL.

Is there a way to edit for this?

I can see how to do it by editing the .htaccess file but I am handing the site to others who will be less able to do that.