I just asked my Ped yesterday for my 6 month old. She said until 8-9 months, she would drink 28-32 oz a day but around 8-9 months many kids start to self-wean as they eat more food. If he wants to eat, let him eat. She said the minimum my LO should eat if she isn't interested in formula is 20 oz, so I'd say make sure he gets at least that in a day, but if you want to give him more food food, do that.
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