C-Sharp Process.Start und SubProcesses

var return = Execute.This(_uninstallString);

public static class Execute
    {
        public static int This(string startExeFilePath)
        {
            int toReturn                            = 0;
            System.Diagnostics.Process p            = new System.Diagnostics.Process();
            System.Diagnostics.ProcessStartInfo psi = new System.Diagnostics.ProcessStartInfo();
            psi                                     = GetProcessInfo(startExeFilePath);
            p.StartInfo                             = psi;
            try
            {
                
                p.Start();
                while (ProcessHasRunningChilds(p.Id) == true)
                {
                    System.Threading.Thread.Sleep(2000);
                }
                
                p.WaitForExit();
                toReturn = p.ExitCode;
            }
            catch (Exception e)
            {
                MessageBox.Show("Es ist ein Fehler aufgetreten! Sehen sie:" + Environment.NewLine + e.Message, "Fehler", MessageBoxButton.OK, MessageBoxImage.Error);  
                toReturn = 1;
            }
            
            return toReturn;
        }

        public static bool ProcessHasRunningChilds(int parentProcessId)
        {
            bool toReturn = false;
            String myQuery = string.Format("select * from win32_process where ParentProcessId={0}", parentProcessId);  
            ObjectQuery objQuery = new ObjectQuery(myQuery);
            ManagementObjectSearcher objSearcher = new ManagementObjectSearcher(objQuery);
            ManagementObjectCollection processList = objSearcher.Get();


            if (processList.Count > 0)
                toReturn = true;
            
            return toReturn;
        }

        public static System.Diagnostics.ProcessStartInfo GetProcessInfo(string startExeFilePath)
        {
            System.Diagnostics.ProcessStartInfo psi = new System.Diagnostics.ProcessStartInfo();
            string _startExeFilePath    = Regex.Replace(startExeFilePath, @"([""])", "");  
            string extension            = Path.GetExtension(_startExeFilePath);
            switch (extension)
            {
                case ".vbs":  
                    psi.CreateNoWindow  = false;
                    psi.UseShellExecute = true;
                    psi.WindowStyle     = System.Diagnostics.ProcessWindowStyle.Normal;
                    psi.FileName        = "cmd.exe";  
                    psi.Arguments       = "cscript " + (char)34 + _startExeFilePath + (char)34;  
                    break;
                case ".cmd":  
                case ".bat":  
                    psi.CreateNoWindow  = false;
                    psi.UseShellExecute = true;
                    psi.WindowStyle     = System.Diagnostics.ProcessWindowStyle.Normal;
                    psi.FileName        = "cmd.exe";  
                    psi.Arguments       = (char)34 + _startExeFilePath + (char)34;
                    break;
                case ".ps1":  
                    psi.CreateNoWindow  = false;
                    psi.UseShellExecute = false;
                    psi.WindowStyle     = System.Diagnostics.ProcessWindowStyle.Normal;
                    psi.FileName        = "powershell.exe";  
                    psi.Arguments       = (char)34 + _startExeFilePath + (char)34;
                    break;
                case ".exe":  
                    psi.CreateNoWindow  = false;
                    psi.UseShellExecute = false;
                    psi.WindowStyle     = System.Diagnostics.ProcessWindowStyle.Normal;
                    psi.FileName        = (char)34 + _startExeFilePath + (char)34;
                    break;
                case ".msi":  
                    psi.CreateNoWindow  = false;
                    psi.UseShellExecute = false;
                    psi.WindowStyle     = System.Diagnostics.ProcessWindowStyle.Normal;
                    psi.FileName        = "msiexec.exe";  
                    psi.Arguments       = "/i " + (char)34 + _startExeFilePath + (char)34 + " ALLUSERS=1, RESTART=REALLYSUPPRESS /norestart MSIRESTARTMANAGERCONTROL=Disable";  
                    break;
            }
            return psi;
        }
}