Why or how would a chiropractor "adjust" young children, being that young children are so flexible anyway?

Health Hooey. Imho this is medical quackery at it's worst. Although some chiropractics claim to be pediatric specialists, neurologists, evidenced based medicine does not bear this out. Bony manipulation also doesn't cure allergies, autism or adhd. There is clinicial evidence that chiropractic medicine can be useful in the treatment of adult low back pain. There is some controversy w docs who care for adults.
Never. There are no pediatric conditions that any chiropractor should ever be involved with. They cannot diagnose disease in children, should never take an x-ray of a child, should never touch a child and never, never do the deep massage they practice which can be very dangerous in a child. Beware.
To build a practice. I am aware of some "practice builder" CD's that were sold on line by chiropractors.They suggested that offering to adjust kids was a good way to get the family involved & have a constant supply of patients. No science, just salesmanship. Most straight chiropractors cringe at the idea that these folks are out there.