Get CheckBox Controls From GroupBoxes

I have 8 group boxes on a form

The group boxes have checkbox controls on them.

I need a way to traverse all of the group boxes to find all of the checkboxes.

I can traverse one group box at a time (shown below) 

              foreach(Control g in groupBox1){

                if (g is CheckBox)
                {
                    
                    listBox1.Items.Add(g.Name.ToString());
                }
              
            }

but not more than one at a time.