Because it is healthy. I believe that the natural state for children and adults alike is to be happy and at home in our environment. Young children are happy and at home in their environment, but at some point in their lives, worry, fear, depression, greed, anger, and other negative emotions emerge. For some, negative emotions become predominant and displace their natural state of happiness. The teachings and technology of Kundalini Yoga, when learned and practiced, helps children maintain their natural state of happiness and balance. Kundalini Yoga helps adults maintain or regain natural happiness and health. So, the idea behind Kundalini Yoga for kids is to teach them the tools to stay or become fully happy, health, and whole as they grow and mature into adulthood. In adulthood, these yoga children will have the tools to be balanced adults, and to attain wisdom and bliss inwardly and in their relationships with others.
The middle school or high school child who is on the first string of a basketball, hockey, soccer, baseball or other team, who completes a Kundalini Kriya will get the same physical work out obtained in her or his sport, but will also get an added dimension of self awareness beyond body and mind. This added dimension allows them to learn how to create focus and create calmness for themselves. The classmates of the first stringers who do not try out for the team because of the certainty of sitting on the bench, will get those very same benefits and will also get the bonus of that stuff we call self-esteem. All, the first stringers, the bench sitters and those who do not aspire for team sports, will become physically fit, mentally focused, and consciously aware of themselves from within and consciously aware of others. All learn that they are bountiful, beautiful, strong, and kind, and life is good.
For the kindergarten through the fifth grade crew, Kundalini Yoga exercises are presented with age appropriate creativity. The exercises within Kundalini Yoga will ready children for athletics and academics, just as Kundalini Yoga assists adults with techniques for clearing their minds, focusing and being open at work and at play.
The type of physical exercise within many Kundalini Yoga exercises are beneficial to the brains of kids (and adults and seniors). Studies have demonstrated that certain arm and leg and body movements will rehabilitate or heal those with physical reflex disabilities rooted in the brain stem or thought processing disabilities. These same arm and leg and body movements boost brain stem reflex reactions and the brain processing power of kids and teens (and adults and seniors too) who have no disabilities. These same or similar arm and leg and body movements are within Kundalini Yoga exercises. Just Google the topics of PACE or brain gym or archetypal reflexes.
Yogi Bhajan, who brought Kundalini Yoga to the United States, is quoted as saying: "Children are super-sensitive, full-fledged people, with high potency antennae which record every vibration within their vicinity, completely and very deeply."
I believe that Yogi Bhajan's observation is correct. Because children are like sponges, absorbing everything around them, children will readily learn the technologies of Yoga and use the technology to help themselves and others through their entire lives.