I don't believe you can get to the children from the process object directly - although the relationships exist, I think thats one of the hidden ones which you can't access through query designer.
You may be able to use a filter to put it at the bottom of a window, but not on the query results view - which I think is what you want.
I do query this relationship so I can identify all the children of a parent in a query. Base the query on Incident Incident, and you can get to both the parent and children Incident. If you use the Group By on the Parent ref, you will be able get to a list of the chilren. you can reference attributes from both the parent and the children in the query results view as well as the Preview Pane
The window contents if fine and its the Query (to be used on a dashboard) where I want to see the information. As I thought it was a 1-many relation you could just drag it across, however not so!
Apart from using the Incident and Change objects for separate queries I cant see any other way of achieving it. Another slim possibility is a calculation, however wouldn't know where to start!