wp_list_pages – show pages immediately 1 level below current level

If your “Events landing page” is a proper WordPress “Page”, which I assume it is, then I think that all you need is:

$children = wp_list_pages("title_li=&child_of=".$post->ID."&echo=0&depth=1");

1. On the landing page, you should get the four regions
2. On a regions page you should get the regions children
3. On the individual child pages you’d get nothing

I am not sure if #3 is what you want but #1 and #2 are correct, if I understand the question.