It's very similar to a push-up, but his pelvis stays on the floor, so that his lower back is arched.
one surprising thing that helps relieve lower back pain, is it stretching all the muscles in the legs, especially the ones on the inner thighs, the abductors and adductors. Many times chronic low back pain comes from having tight leg muscles. stretching those out helps relieve the tension on the pelvis that the low back muscles have to compensate for.
Always remember, you should talk to your chiropractor before starting your son and any stretching or exercise routine. Also, stretching is good, and necessary. But it does not replace what chioropractic does for the spine.
Take care and be well,
Dr. Eric Miller