Breastfed babies usually takes about 600ml - 900ml of BM in 24h on average.
And yes, I have heard that BM intake for babies 1mo - 6mo stays roughly the same. It's the BM composition that changes to suit their needs. I also understand this is more true for mothers who latch their babies, since there are more interactions between the babies saliva and the "sensors" in the nipples. I can't say the same for mothers who pump exclusively. But that's the general guideline.
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