Launch games for kids

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C#

hi all
i already create form and TopMost without any problem but if i run game or notepad or anything my form on top , my question is how to make excute for my run exe file to be top
my form .. using c# 2015

FormBorderStyle = System.Windows.Forms.FormBorderStyle.None;
            WindowState = FormWindowState.Maximized;
            this.TopMost = true;
            Process.Start("C:\\");

What I have tried:

FormBorderStyle = System.Windows.Forms.FormBorderStyle.None;
            WindowState = FormWindowState.Maximized;
            this.TopMost = true;
            Process.Start("C:\\");
            Process.Start = TopMost;