One to 4 years: A damp down snowsuit or cotton jacket pulls heat away from the body, so once your child starts playing outdoors, choose water- and wind-resistant material. Outerwear doesn't have to be bulky to be warm. Thin materials, such as Quallofil or Thinsulate, protect against cold. The overall fit of the suit or jacket, including closures at wrists and ankles, should be snug (the neck should be high but comfortable) to keep out wind and snow; bibs on overalls should come up high on the chest and back.
Source : http://www.cnn.com/2012/12/06/living/parenting-dress-your-baby-for-winter/index.html