Kendo UI for angular treeview get Children data

Kendo UI for angular -Tree view with checkbox need to read the children nodes on parent node selection without node expand

There is working prototype available but it works on expanded node only

https://www.telerik.com/kendo-angular-ui/components/treeview/checkboxes/#toc-modifying-the-checked-state

On checked on parent node -instead of showing Checked keys: 0 its should display Checked keys: 0,0_0,0_1,0_2 how it works after node expansion.