Is it just black diarrhea? If it has a coffee ground look to it I stongly sugest you go to see a dr. Waiting may not be good. Good luck
I think before you guys do anything, wait and see what color his waste is in a few day from now. Also, if he drank Pepto Bismol, it will turn waste black. You can always go to the county health department and be seen there for very little cost.