Enable\Disable menus of MDI Parent

[coolarian]

Hi,
I have an C# MDI application. There are three mdi childs, mdiFormA, childB and childC. childA is loaded in the parent by default as below:
private void TestingMenu_Load(object sender, EventArgs e)//mdiParent load
{

mdiFormA objA = new mdiFormA();
objA.MdiParent = this;
objA.Show();
//this.formAToolStripMenuItem.Enabled = false;

}

mdiFormA can also be opened from the menustrip menu as:
private void formAToolStripMenuItem_Click(object sender, EventArgs e)
{

if (!menuEnabler.ParentIsActive)
{
mdiFormA objA = new mdiFormA();
objA.MdiParent = this;
objA.Show();
//this.formAToolStripMenuItem.Enabled = false;
}
else
{
//this.formAToolStripMenuItem.Enabled = true;
}
}
Similarly mdiFormB and mdiFormC can also be opened from the menu_clicks.

What I need to do is when the application is launched and mdiFormA is successfully loaded, the menu item to open mdiFOrmA bcomes disabled and at this instant menu items for childs A and B becomes enabled. When mdiFormA is closed/disposed, the menu item to open mdiFormA becomes enabled but the menu itms to open mdiFormB and mdiFormC becomes disabled.

I have tried to implement this mechanism by making all the menus of parent public and then doing something like this in mdiFormA:
TestingMenu obj = new TestingMenu();
obj.formAToolStripMenuItem.Enabled = false;
obj.formCToolStripMenuItem.Enabled = true;
obj.formCToolStripMenuItem.Enabled = true;

[coolarian]

Continuing from my last post:
This doesn't work as I think this is not a correct approach but since I am new to programming I can't figure out how to make this working. I think I can do some event driven programming to implement this. The user wants to have exactly this type of fucntionality like visually see the disabled menus.

Please anyone, any help is welcomed.
Thanks.