In D7, how do you create a View showing all the child groups of a group in Organic Groups?

I've started off with the 'OG Extras Groups' view, which shows all groups. I thought it'd be simple to then just add a filter for 'Content: Parent group', and that would show the children of a selected group. It returns no results, though.

I've tried all sorts of relationships but can't get the child groups to show. This thread is the only information I've found: https://www.drupal.org/node/159988. The explanation is for D6, though, and I can't see an easy translation to D7.

I've only got five groups so I don't need to set a contextual filter - I can hard code the parent group value (either name or ID).

How do you create a View showing all the child groups of a group in Organic Groups?

I've started off with the 'OG Extras Groups' view, which shows all groups. I thought it'd be simple to then just add a filter for 'Content: Parent group', and that would show the children of a selected group. It returns no results, though.

I've tried all sorts of relationships but can't get the child groups to show. This thread is the only information I've found: https://www.drupal.org/node/159988. The explanation is for D6, though, and I can't see an easy translation to D7.

I've only got five groups so I don't need to set a contextual filter - I can hard code the parent group value (either name or ID).