Spending time outside is important for children to develop physical skills, learn and develop through experience and they are more likely to catch a cold, and other bugs, indoors in winter as people bring viruses and bacteria in with them and then may pass them around, especially if the space is not well ventilated. If children are outside, they are less likely to share their bugs. Furthermore, fresh air can support the healing process, hence going outside, dressed appropriately, can be good for you when you are ill (unless you are advised not to by a medical professional).