How much pedilyte to give a 3 month old?

Be careful: About giving pedialyte to your infant without a pediatrician helping to guide you. They can quickly get dangerous electrolyte problems. Please check in with your pediatrician. In developing countries, parents will feed their dehydrated children pedialyte one spoonful at a time (5 mL). But again, your child needs to be closely monitored by his pediatrician.

Stool replacement?: Pedialyte is often recommended for infants to prevent dehydration. Those with diarrhea are often offered 1-2 ounces after every loose stool. Those who are refusing to eat or drink because of illness, or recovering from an illness associated with vomiting, are usually offered full volume replacement (substitute the same amount of Pedialyte as baby would normally take in formula or breast milk).

Weight dependent: How much does he/she weigh? Is this for rehydration? Has she been vomiting? She needs to void every 4-6 hrs to know if well hydrated. I would say maintenance fluid alone for a child weighing 5 kg would be 40 ml/kg/hr, so about 500 ml at least minimum for the day. More is better, but better to drink in small amounts like tablespoons of fluid.