Thingworx - Grid Widget ChildData property - How to make it expandable?

Hello,

Im sitting with the grid widget in a mashup and have bound an infotable to the data property and have now also bound other data that is suppose to be "child" data to the first data property. How do I successfully make the expandable functionality in the grid widget work? I've tried to bind the "child" data to the ChildData property of the grid widget and the "+" buttons are showed in the mashup but nothing happends (not expanding/showing child data) when i click the "+" buttons. Additionally, no clear expandable event seem to exist for the grid widget. Anyone here with Child data configuration knowledge for grid widget in Thingworx? 

Thanks in advance.

Sincerely,
Pontus Koontz