Sleep sacks that have a higher TOG, and that are made of fabrics like fleece and Sherpa are perfect for the winter months or cold climates. There are a few models that are made of wool also that would be warmer than just regular cotton or polyester materials. You can also always put thicker clothing on the child before putting them in the sleep sack or wearable blanket to increase their body warmth retention inside the item. We do give the TOG ratings when it was given in the product descriptions for you to reference when purchasing.