Setfocus

I have a main window with two other window inside of it sortof like Parent and childs. I want to toggle the focus from either child. I place a Toggle in the menu of the parenet with pop-up Schematic and Trend which is the name of the two child windows. I try using SetFocus(hwndTrend) or SetFocus(hwndSchematic) but it does not work. I can use DestroyWindow(hwndTrend etc and it work. I know I'm not very clear on what my problem is but I'm a beginer in Visual C++. and poor at english

what kind of windows are the inner ones?