怎么让子窗体只在父窗口中弹出？

子窗体 Form2

Form2 kk=new Form2():
kk.show;

楼上这样恐怕不能实现哦
From2 sub = new From2 ();

//确认子窗口惟一
foreach(System.Windows.Forms.Form ff in this.MdiChildren)
{
if(ff.Name == "子窗口name")
{
ff.Activate();
ff.WindowState = FormWindowState.Maximized;
return;
}
}
//设置父窗口
sub.MdiParent = this;

sub.Show();

谢谢啦