Typing RD /S /Q <Drive:>\FolderName will delete all files, sub-directories and the <Drive:>\FolderName also. If you wish to not remove the target folder, create DELTREE.BAT in your path:

 
@echo off
if \{%1\}==\{\} @echo Syntax: DelTree Folder&goto :EOF
if not exist %1 @echo Syntax: DelTree Folder - Folder %1 does not exist.&goto :EOF
pushd %1
if %ERRORLEVEL% NEQ 0 @echo Syntax: DelTree Folder - Folder %1 does not exist.&goto :EOF
del /q /f "*.*"
for /f "Tokens=*" %%i in ('dir %1 /B /A /AD') do rd /s /q "%%i"
popd
To delete all the files and sub-directories in <Drive:>\My Test Folder, type:

DELTREE "<Drive:>\My Test Folder"