If you observe a baby, from the time it is born to the age of three, it does all the yoga postures. You only need keen observation to recognize this, not a yoga instructor.
When a baby is born, it is born in a particular mudra, which is called Aadi mudra (thumb tucked into palm and other fingers wrapped into a fist) in the science of yogic texts.
When babies sleep, if you notice, they sleep with their hands in Chin mudra (tip of thumb and fore finger touching and other fingers are extended), and Chinmayee mudra (tip of thumb and fore finger touching and other fingers are rolled in touching the palm).
They also do the Merudanda mudra (thumb pointing up and other fingers rolled in) when they suck their thumb.
A mudra (hand posture) stimulates certain parts of the brain and certain parts of the body. So babies do all these different mudras.
If you notice, whenever someone feels cold, the first natural tendency is to hide the thumbs under the arm-pits, to keep the thumbs warm. Actually, in yoga, the thumbs are very important. It is said, if you keep the thumb warm, the whole body is kept warm.
In yoga, it is also said that the tips of our fingers are energy points. Similarly, our ears are also energy points. In Ayurveda, these are called Marma points; the secrets points of energy in the body. When these points are stimulated, they release energy into the system. This is the tradition of Ayurveda.
Coming back to observing children, if you notice they also do the Cobra pose, where they lie down on their stomach and lift up their neck. Then they do the Boat pose, where they lie on their backs with their hands and legs off the ground.
They do almost all the yoga poses before the age of three. We simply need to observe them. Also, the way children breathe is different; they breathe from the belly.
Every emotion has a corresponding rhythm in the breath. You may have observed that when you are happy, your breath moves in a different rhythm as compared with when you are unhappy. The temperature, speed, length and the volume of your breath is different. (This is even taught in theater classes; how to express different emotions by changing the breath.) So, our emotions are linked to the breath and to some parts of the body.
Excerpt taken from the article by Sri Sri Ravishankar, the link to view the complete article is given below: