It is a little simpler to do this task in our upcoming 7.4 release as there are better APIs exposed to handle some of the intricate code.
Below is our Hierarchical Demo sample modified with a PreviewMouseDown event handler to display both parent and child information on the cell that is about to be clicked. It is coded to work with 7.3 code. There is a commented handler that will work with the 7.4 code.
CS_23e701ea.zip