Personally I would set it up a bit more generic, i.e. a recursive method.
public Control FindControlRecursive(Control control, string id)
{
if (control == null) throw new ArgumentNullException("control");
if (control.ID == id) return control;
foreach (Control child in control.Controls)
{
Control c = FindControlRecursive(child, id);
if (c != null) return c;
}
return null;
}
And then you can call it like this
CheckBox chkbx = (CheckBox)FindControlRecursive(superTabControl1, "idofcheckbox")