Run the Child Test Item hold by a TestItem

Hi,

I have added a New Test Item and under that Test Item I have added Child Test Item. 

as per the link - https://support.smartbear.com/testcomplete/docs/reference/project-objects/project/testitems/testitem.html

https://support.smartbear.com/testcomplete/docs/reference/project-objects/project/testitem/index.html

Test Organization like -

Regression Test Pack -

             Login Test

                      Valid User

                       Invalid User

                New Order

                         Partial Order

                         Complete Order     

Here I did not find any method to access Child Test Item , like to access Valid User , Invalid User

Below code work - 

Set TestItems = Project.TestItems

Set TestItem = TestItems.TestItem(0)　

log.Message TestItem.Name

but this not work -

Set TestItems = Project.TestItems

Set TestItem = TestItems.TestItem(1)　

log.Message TestItem.Name

how can access Test Item along with all childs and child of Childs