I don't see how it's good or bad from a reproduction point of view. Unless pregnancies at 10 have higher rates of miscarriages, deformities or still births etc, then I don't see how it's any better or worse than reproduction at 15, 20 or 25. I haven't looked this up, but if pregnancy is possible, I would imagine breast-feeding postbirth is also possible, so the baby won't starve neither.
Only argument that I see could have a solid backing to it would be the effect the weight of a child would have on a growing teenager's backbone - but that's hypothetical (unless you can find something to back it up), and when I remember the weight of backpacks we had to carry in highschool, insignificant.
To direct this back to my intentions, I don't see any problem with your claim that it "wouldn't be a good idea under any circumstance" - just that I wish to clarify that I don't believe it to be a "bad" idea neither.