Why do children have to drink whole milk until 2 years of age?

I have a 14-month-old daughter. I want to know why children should be on whole milk until 2 years old when the only difference is the amount of fat.

You've got the answer right there: little children need the extra fat. It's necessary not only for general growth but also for the fatty acids that are so critical for brain development in the early years of life. Human milk has the highest cholesterol content of any milk in the animal kingdom because humans have the largest brains and the most immature brains at birth. Alternative milks given to human infants also need to be relatively high in fat, too. Infants and toddlers under 2 should have half of their calories in fat, not the 20 per cent to 30 per cent recommended for older children and adults. Milk is an important source of the fat calories that support hair and skin health and the absorption of certain vitamins, too. Keep her on whole milk for at least the next 10 months and longer if directed by her GP.