What should I do if my child cannot keep hydration fluid down?

Dehydration. Make sure that your baby is well hydrated you can try with small amount of fluids every 15 minutes and if your baby does not tolerate please take him to the doctor.
Go to the ER. Make sure you're giving it in little sips, and don't dilute it-- use it the way it comes, premixed from the bottle. But if your child has frequent vomiting and cannot hold down rehydration solution, it's time to head to the emergency room.