Putting 3 month old exclusively on cows milk. What kind of damage can this cause?

I've heard that infants are NEVER supposed to have whole milk til atleast after 12 months and my SIL just put her 3 mo. old daughter on whole cow's milk because she was having problems with the formula she was on. Her grandmother (the baby's great g-mother) told her to put the baby on cow's milk... show more I've heard that infants are NEVER supposed to have whole milk til atleast after 12 months and my SIL just put her 3 mo. old daughter on whole cow's milk because she was having problems with the formula she was on. Her grandmother (the baby's great g-mother) told her to put the baby on cow's milk because that's what she had to do when her daughter had problems with formula. My SIL is being told way too many old wives tales that can be downright dangerous for her baby. I keep telling her not to listen and to talk to her doc but all she says is "well, they raised their families and everyone is still alive, and "milk is cheaper anyways". But the majority of that family has all kind of medical issues and learning disabilities (which may have started as babies). What kind of harm can this cause the baby? ie: what kind of developmental problems can/may she possibly develop.
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