Just use the createWindow function.
For a child window this would be something like:
newChild=createWindow(0,0,200,200,"Child Window",WINDOW_NORMAL,0,0,0)
In BlueGUI v1 there was a bug where child windows could not go outside of their parent, which is not proper windows behaviour.
However, if you want to force the child window to stay inside of the parent, you can use setParentGadget - this is technically a bug, but I have been asked not to fix it!
BlueGUI:Windows UI Plugin - All the power of the windows interface in your DBPro games.