If a child request is the "last" one in the child request tree (i.e., it is not a "parent" to another request), it can be deleted using the context menu item "Delete Request".
If you need to delete a chain of child requests, you must call the context menu from the "parent" request (external, internal, or child) and select the item "Delete Child Requests".
After this, a window with information about the number of deleted child requests will appear on the screen.

If a request has several child requests forming a request tree, the context menu item "Delete Child Requests" will delete ALL child requests simultaneously.