A child having a history of profuse watery diarrhea with poor oral intake and not passed urine for 2 days is suffering from diarrhea with dehydration and probably an acute renal failure of pre-renal types.Here the best choice is intravenous fluids.If IV access not possible, then you can give feed through Ryle's tube or intraosseous fluid.(Refer: Nelson's Textbook of Pediatrics, SAE, 1st edition, pg no. 2704 - 2705, 2714 - 2723)