disable batch file in csharp

You can do this via the registry:

key:   HKEY_CURRENT_USER\Software\Policies\Microsoft\Windows\System
Name:  DisableCMD
Type:  REG_DWORD
Value: 1

This disables the command prompt, and the use of batch files. To reverse, set the value to 0.
You can set this in software by using teh registry modifiers, but I would be tempted to do this via the Group Policies Editor instead:
1) Click Start, Run, type gpedit.msc and click OK.
2) Navigate to User Configuration \ Administrative Templates.
3) Right click, and select "Add Template"
4) In the dialog, select "System" and press "Add". Press "Close"
5) Select the system template in the left hand pane, and "Prevent access to the command prompt" is one of the options in the right hand pane.
If you look, you will find others you should find relevant for your cafe as well - this is partly why I would recommend this route rather than just writing C# software to do it!