According to the search results, the ideal tog duvet for a toddler in winter is between 4.5 and 7.5 tog. However, the specific tog rating depends on the temperature of the childs bedroom and their personal preference. It is recommended to start with a 4-tog duvet once the child reaches the age of one, and then gradually increase the tog rating as they grow. It is also suggested to keep the child sleeping with a lower tog duvet as long as possible, as they will be most comfortable with it. On cold nights, it is recommended to have a blanket that the child can sleep under as well as the duvet for extra warmth.