how to change properties of child form controls in parent form

Question

I have a Mdiparent form containing a button and some child forms. How is it possible to change backcolor of all textboxes in all child forms when clicking the button in parent form?

Answer 1

This the ChilForm;

        public ChilForm()
        {
            InitializeComponent();
        }

        public void ChangeTextboxColor() 
        {
            textBox1.BackColor = Color.Yellow;
        }

And this is Parent;

        ChilForm frm = new ChilForm();

        public Parent()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            //Shows the child
            frm.Show();
        }

        private void button2_Click(object sender, EventArgs e)
        {
            //Changes color
            frm.ChangeTextboxColor();
        }