My 3 year old is vomiting up mucus has really bad diarrhea what should i do?

Gastroenteritis: Try to control the vomiting with electrolyte replacing fluids. Once vomiting is under control begin a bland diet, nothing greasy or fried. Stay away from milk and juices. If you feel the baby is getting dehydrated take your child to the er for treatment.

Vomiting & diarrhea: Try to assess if your 3 yo is getting dehydrated or not. Signs to look for: no tears when crying, dry mouth or thick saliva, weak cry, body weakness - trouble getting up or wlaking, sleeping a lot, fever, not urinating in last several hours, not able to keep down water or pedialyte. If any of the above are present, bring your child to his pediatrician, urgent care center or hospital ed.