Child pose, also known as Balasana or resting pose or resting child pose or little piece of heaven. As the name suggests, it is a relaxing and restorative posture. It relaxes the spine, helps to calm down the nervous system, brings the heart rate down and also helps to relieve constipation. It stretches back, hips and thighs. It calms the brain and helps to reduce stress and fatigue.
Pregnant women should not attempt it. Also avoid if you have knee problem. It is also to be avoided if you have diarrhea.
Try to press your chest on your knees and hips should touch the heels.
It is a counter pose for many asanas. Specially, when you do inversions such as headstand or Sirsasana, you should rest in child pose for some time. It will help to balance the flow of blood towards the head.
There are few variations you can do with hands. You can stretch them forward or keep them close to you. You may place the hands back, close to your hips or interlock your hands and take them up as shown in the last picture.