How to disable the MDIparent form when a child form is activ

Question

Hi there
Am a new student in C# and am using Microsoft Visual C# 2013.
My aim is to
i. open a child form inside its MDIparent form
ii. disable the MDIparent form when the child form is active/opened

it was easier in VB.net with
frmStuDetails.ShowDialog()

I have tried

1.
MyChildForm childForm = new MyChildForm();
childForm.ShowDialog(this);

Result....but the problem is that the child form doesn't open within the MDIparent form/container

2.
under MDIparent call button
frmViewStuList childForm = new frmViewStuList(this);
childForm.Owner = this;
childForm.Show();

under child from Activated
 if (this.Owner != null)
  {
    this.Owner.Enabled = false;
  }

under child form Deactivate
 if (this.Owner != null)
 {
   this.Owner.Enabled = true;
 }

Result.....it makes the child form active  but freezes the MDIparent when the child form closes

3.
ChildForm child = new ChildForm();
child.Owner = this;
child.Show();

// In ChildForm_Load:
private void ChildForm_Load(object sender, EventArgs e)
{
  this.Owner.Enabled = false;
}

private void ChildForm_Closed(object sender, EventArgs e)
{
  this.Owner.Enabled = true;
}

Result ....It seems to be the best option but the child form doesn't open within the MDIparent

Please help if you have any other idea
Thanks