In Rally we have the following story structure:
Parent Story 1
|__ Sub Story 1
| |__ Child Story 1
| |__ Child Story
If you wanted to get a list of a parent story's children to see what release they fall in you could use the following query.
(Parent.Parent.FormattedID = ###PUT THE FORMATTED ID HERE###)
If you want to experiment in your browser you can try the following URL.
https://rally1.rallydev.com/slm/webservice/1.26/hierarchicalrequirement.js?query=(Parent.Parent.FormattedID=###PUT_THE_FORMATTED_ID_HERE###)&fetch=Release&pretty=true
If you knew that the children stories would all be in the same release you could put a &pagesize=1 and look at the release for that single returned story while saving a bit of bandwidth.
One of the weird parts about this query is that you will have to know how deep the stories you want to retrieve are from the parent you are interested in. In the case of your example your hierarchy is two deep so in the query you use the Parent.Parent of the stories I am trying to retrieve.