Pranayam was practised by sages centuries ago in India. Now a sage (
Swami Ramdev) has simplified the technique, so ordinary people can understand how to do it, and people are reaping benefits. Basically the body can heal from inside, when the cells are energised with the extra oxygen going into the blood with pranayam.
Try to do it in a fun way with the child, and he will enjoy it.
Keep a note of what you notice, regularly, as it will help you explain to others, what you are experiencing.