Binding .MVC Grid to Heirarchical objects using JSON

 Can someone provide me with a simple example of doing this?  I want to load parent and child records all at once and bind to them.  I have it working now with just the parent records but whenever I try to click the plus sign to view the child records I get cryptic errors like "0x800a138f - JavaScript runtime error: Unable to get property 'length' of undefined or null reference".  The JSON is definitely returning correctly but I'm not sure what the grid is unhappy about.

I have been looking through the Ignite UI examples but haven't been able to get this working.