Layer 3 is the outer layer and should consist of a water repellent layer to protect the child from wind, rain and snow. The garment needs to have a good breathability and let out the moisture transported from the other layers. The breathability depends on what activity the child will be doing, if the child sweats a lot and the garment doesn’t breathe, it will result in the child getting cold fast.
Important complements for the three layer principle is hats, mittens and shoes that prevents body heat from escaping. When it comes to mittens, layering is a good approach here as well. An inner mitten will keep the warmth and an outer water repellent mitten will keep the hands dry and warm. A good alternative in cold conditions is a lined mitten. It is also important to make sure that the socks are dry, woolly socks are by far the best option, but regular socks works fine too as children rarely sweat at the feet. As for shoes, get a pair with a good, rough patterned sole to avoid slipping.