Development Economics Minor for CS Major
I agree with the others that it makes sense to explore what interests you at this stage. CS is already a strong major and you will be forced to specialize more later on. A few points in favor:

I don't think anyone pays too much attention to your minor, to be honest. I would weigh the transcript more heavily than the precise name of the major or minor, so if your coursework shows a strong foundation in math/stats/CS classes then I see no problem with having an additional interest.
Economic thinking is an interesting and new perspective in and of itself which could benefit you as an intellectual. I think it would broaden your horizons and give you an approach to modeling that many CS majors won't have. The intersection of econ + CS is also growing in popularity.
There is a decent community of emerging around computing for development. Some resources you might find useful are:
https://acmcompass.org/
https://didl.berkeley.edu/
https://crcs.seas.harvard.edu/
https://www.ml.cmu.edu/academics/joint-phd-mlpp.html
Maybe you can find some profiles that look like yours for inspiration.

That said, I agree with the commenters that math and statistics will be very valuable to you if you pursue ML at a higher level. So it would be good to load up on these courses now if you plan to move on to a competitive graduate degree.
Also, if by &quot;graduate school&quot; you mean PhD, I believe research would be much more important than adding a single line to your CV as a minor. Perhaps you could do some research at the intersection of computer science and development?