What Causes Passing Of Dark Stool And Vomit Of A 17 Month Old?

Hello I have a grandson who is 17mts he went to the dentist today around 5:00p.m. my daughter just called me saying he s vomiting dark brown and he pooped dark brown. He s been vomiting since 10:00 he doesn t want to keep anything down. What do you think we should do? Take him to the hospital or keep trying to give him something to drink and see if it stops?