You might want to consider two portals a "master" portal to Parent and a "slave" or "detail" portal to Child. Using scripts and buttons, when you click on a portal row in the portal to Parent, just the children of that one parent appear in the detail portal. See this thread for details: Need layout solution for nested portals...
If you only need to list data from a single field in Child, you may want to define a calculation field in Parent with this expression:
Subsitute ( List ( Child::childField ) ; ¶ ; ", " )
This produces a comma delimitted list of values from ChildField in a single field.
In FileMaker 12, the same result can be produced with ExecuteSQL.
Thanks PhilModJunk. The substitute calc is perfect in this particular case. Will also read through the other post about portals in case it helps me elsewhere in my solution.