Control's location on an MDI child form

Recursively follow the Controls collection, looking at each items Location:

Control findLoc(ControlCollection controls, Point loc)
   {
   if (controls != null)
      {
      foreach (Control c in controls)
         {
         if (c.Location == loc)
            {
            return c;
            }
         Control f = findLoc(c.Controls, loc);
         if (f != null) return f;
         }
      }
   return null;
   }

Do note that the Location property is relative to the container, not the screen - so you may need to alter the target loc to allow for that when you recurse into it's Controls collection.