As a paediatrician, I actually was taught that you could tell if children were warm enough by touching their skin. If they felt warm then they were wearing enough clothes, and if they felt cool or their skin was mottled (bluish-pink), then they needed more clothes. It was simple. I was also a parent that had her 2 year-old child playing outside in the rain wearing only a diaper. I actually thought he was okay because his skin felt warm!
Warmth is probably one of the greatest gifts we can give our children. Not only the warmth of our love but also keeping their physical body warm. Children are developing their bodies especially during the first 7 years of their lives. An infant and a young child will always feel warm unless they are on the verge of hypothermia because they have an accelerated metabolic rate. If we don't provide them with the layers of cotton, silk, and wool to insulate their bodies, then they must use some of their potential "growth" energy to heat their bodies.
This same energy would be better utilized in further developing their brain, heart, liver, lungs etc. In addition, being cold decreases immunity. We are all more susceptible to the germs and viruses that are always around us when we are wet and cold. When our body has to expend extra energy to keep warm then less energy is available to "fight" off infections.
So the question becomes, how do we get our children to wear jackets? One can develop the habit of always having children put on a hat and coat when they go outside during cool weather. One can also try telling children that they will actually run faster and have much more energy to play if they wear a coat. If they don't wear a coat then their body has to expend a lot of energy just warming them up, and they will have less energy to build muscles and less energy to play.
Finally, the type of clothing our children wear also makes a big difference. Polyester pajamas don't breathe and children will often wake up sweating. Even polyester jackets will not insulate a child from the cold as well as layers of cotton, silk, or wool. When children sweat while wearing polyester that sweat is trapped against their body and they eventually become chilled.
So why do children rarely complain that they are cold? Children often are not connected with their body before the age of 7 to even acknowledge or communicate that they are cold. They live in the moment and are so excited and stimulated by all that they see that they don't have the capacity to sense the coldness of their body. This is why children often will play in a swimming pool or ocean until they are literally "blue" denying that they are cold or that they need to come out of the water. So as parents, we have to help our children develop their sense of warmth. By helping them develop this sense of warmth, we are actually strengthening their immunity and laying the foundation for a healthy body and healthy organs in their adult life.