from 1 year around 300/350mls is recommended but this doesnt all have to be as a drink as other sources of calcium, etc count too.
from babycentre:
From one year, milk should still play an important role in your baby's diet, as it provides essential protein, calcium, magnesium and vitamins B12 and B2 (riboflavin). Your baby needs to have a minimum of 350ml (two thirds of a pint) of full-fat cow's milk each day. If he or she becomes reluctant to drink milk, try offering two portions of calcium-rich foods a day. Yoghurt, cheese, tinned mashed sardines, tofu, white bread and chick peas all contain calcium.
from food standards agency:
Children between the ages of one and three need to consume an average of 350mg of calcium a day. About 300ml full-fat milk (three?fifths of a pint) would provide this.
This extract from babycentre is quite good too:
A generation ago milk, for example, was thought essential for children. Now milk is recognised as a food that some children are far better off without; even for the rest, it's only an easy-to-take package of useful nutrients. The valuable proteins, minerals and vitamins that milk contains are in other foods too, especially the many foods made from it. There's no virtue in a cup of milk that isn't in a cup of yoghurt, any more than there's especial virtue in an egg gazing one-eyed off a plate. The milk and egg in the pancake your child enjoys is just as good.