answer:According to this link, “At a year old, formula-fed babies can switch to whole cow’s milk. It is important to use “whole” milk, because children under two years old need fat for brain development.” And according to this link , “When your child is 2, you can probably make the switch to low-fat or nonfat milk, but talk with your doctor before doing so.” When my son was 2, our pediatrician told us to switch to 2%. Then when he was 4, we were told to go back to whole milk because of his weight. Now he’s 8 and we use 2% again.