How long can a child keep the stomach flu? My 2.5 year old has had these symptoms going on three weeks now. We think he is getting over it then Diarrhea starts in again and vomiting. Woke up last night dry heaving. And his poop has that sick smell to it. We have gave yogurt toast Pedialyte sprite you name it. He complains with his little belly hurting quite a bit too but poop has still not been solid its been like water. we even started on probiotics to try and keep the bad germs out it will be a week Wednesday that he has been taking them. Any advice? hate to see my little guy having this stomach problems.