MDI父窗口中控件阻挡了所有子窗口

先建立一个子窗口，然后调用它，让它一直运行在MDI中：
log = new Frm_Log();
            log.MdiParent = this;
            log.StartPosition = FormStartPosition.CenterParent;
            log.ControlBox = false; 
            log.Show();
            log.FormBorderStyle = FormBorderStyle.None;
            log.Size=new Size(ClientSize.Width/2,ClientSize.Height/2);
            //log.Size = ClientSize.Height-10;
            log.Location = new Point((this.Width) / 4, (this.ClientSize.Height) / 4);

重绘时：

private void SMS_HOME_Resize(object sender, EventArgs e)
        {
            log.Size = new Size(ClientSize.Width / 2, ClientSize.Height / 2);
            //log.Size = ClientSize.Height-10;
            log.Location = new Point((this.Width) / 4, (this.ClientSize.Height) / 4);
        }