Typically a scroll widget is used to view a larger widget
(or group of widgets) of fixed size in a smaller window,
giving the user scrollbars to pan to view it.
The exception might be child widgets that should expand on one axis
but not the other, which I'm guessing is what you're doing, and can
be done with something like this:
http://seriss.com/people/erco/fltk/#ScrollableWidgetBrowser