I assume you want to programmatically "check" the child node checkbox. The "CheckedNodes" property of the parent "Tree" object can be used to achieve this. Here's the documentation link to help you out:
Here's some sample code to "check" the child node:
app.Tree.CheckedNodes = [app.Tree.CheckedNodes app.ChildNode];
%app.Tree is the parent Tree object
%app.ChildNode is the tree node that needs to be checked
If you want to "select" the child node and not "check" it, then similarly, the "SelectedNodes" property can be used.
Hope this helps!
