public Form2(bool needInit)
        {
            InitializeComponent();
            _needInit = needInit;
...

private void Form2_Load(object sender, EventArgs e)
{
            if (_needInit)
            {
                Glut.glutInit();
                Glut.glutInitDisplayMode(Glut.GLUT_RGB | Glut.GLUT_DOUBLE | Glut.GLUT_DEPTH);
            }
 ...

private void newToolStripMenuItem_Click(object sender, EventArgs e)
        {
            Form2 newMDIChild = new Form2(true); // первый вызов дочерней формы
            newMDIChild.MdiParent = this;
            newMDIChild.Show();
        }

        private void new2ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            Form2 newMDIChild = new Form2(false); // последующие
            newMDIChild.MdiParent = this;
            newMDIChild.Show();
        }
 ...