怎么关闭已打开的子窗体

如何关闭已打开的子窗体？
我想完成以下的功能：
有一个父窗体frmMain,两个子窗体frmS,frmW.程序启动时frmS以在父窗体中以最大化的形式显示。我想在父窗体中加一个BUTTON1，当击这个BUTTON1后frmS关闭，frmW显示；然后在frmW中建一个BUTTON2，点这个按钮后，frmW退出，frmW重新载入！
这个具体怎么实现呀？能不能给出关键的代码和思路？

[解决办法]
button1.click

foreach (Form childForm in MdiChildren)
{
if(childForm.Name=="frmS")
{
childForm.Close();
frmW f=new frmW();
 f.MdiParent = this;
f.Show();
}
}



然后在frmW中建一个BUTTON2，点这个按钮后，frmW退出，frmW重新载入！ ???
关了从新载入？？？？

[解决办法]
frmW退出，frmW重新载入！？？？？

是不是frmS重新载入啊，写错了吧！
[解决办法]

C# code

/* -----------frmMian----------- */private frmS fs = null;private frmW fw = null;private void button1_Click(object sender, EventArgs e){   frmS f = new frmS();   fs = f;   f.Show();   frmW ff = new frmW();   fw = ff;   ff.Show();}private void button3_Click(object sender, EventArgs e){   if (fs != null)   {      fs.Close();      fs = null;   }}/* --------frmW------- */private frmS fs = null;private void button1_Click(object sender, EventArgs e){  frmS f = new frmS();  fs = f;  f.Show();  this.Close();}
[解决办法]
private void frmMain_Load(object sender, EventArgs e)
{
     frmS fs = new frmS();
     fs.MaximizeBox = true;
     fs.MdiParent = this;
     fs.Show();
}
  private void button1_Click(object sender, EventArgs e)
{
     this.Close();
     frmW fw = new frmW();
     fw.MdiParent = this.MdiParent ;
     fw.Show();
  }
private void button2_Click(object sender, EventArgs e)
{
     this.Close();
     frmS fs = new frmS();
     fs.MdiParent = this.MdiParent ;
     fs.Show();
  }
[解决办法]

我的这个可以通过，而且可以防止打开多个窗体，如果已经打开，就激活他
C# code
public partial class frmMain : Form    {        public frmMain()        {            InitializeComponent();        }        private void 登录ToolStripMenuItem_Click(object sender, EventArgs e)        {            foreach (Form form in Application.OpenForms)            {                if (form.Name == "frmLogin")                {                    form.Activate();                    form.WindowState = FormWindowState.Maximized;                    return;                }            }                        frmLogin login = new frmLogin();            login.MdiParent = this;            login.WindowState = FormWindowState.Maximized;            login.Show();        }        private void 日志ToolStripMenuItem_Click(object sender, EventArgs e)        {            foreach (Form form in Application.OpenForms)            {                if (form.Text == "frmLogInfo")                {                    form.Activate();                    return;                }            }                        frmLogInfo log = new frmLogInfo();            log.MdiParent = this;            log.WindowState = FormWindowState.Maximized;            log.Show();        }        private void frmMain_Load(object sender, EventArgs e)        {            frmLogin login = new frmLogin();            login.WindowState = FormWindowState.Maximized;            login.MdiParent = this;            login.Show();        }    }