If you would like to create the files and directories again, don't run four commands. Run the following two.
New-Item test-dir/child-dir -ItemType Directory -Force
New-Item ./test-dir/file1, ./test-dir/file2, ./test-dir/child-dir/file3
The parameter, Force, creates test-dir when creating child-dir.
Go ahead and delete the entire directory if you want to, without the Recurse parameter. At the confirmation prompt, press Enter (Y is the default response).