The three-layer system is a practical way to dress children for winter. It includes: - **Base Layer**: Worn next to the skin, this layer should be snug and moisture-wicking. Thermal fabrics are ideal for colder regions, while cotton works for mild winters. - **Middle Layer**: Provides insulation by trapping air. Fleece, wool, or knit blends are common choices. - **Outer Layer**: Protects against wind and moisture. Look for jackets that fit comfortably over other layers and allow free movement.