I would definitely recommend Craniosacral therapy for a child favoring one side. There is a real possibility that the baby needs some adjustments of the fascia which can move the bones out of place just a small bit, but enough to cause such.
CranioSacral Therapy is a light touch therapy that is done with the hands to address restrictions in the membranes that surround the brain and spinal cord. Imbalances or restrictions in the cranialsacral system may negatively impact the nervous system and may cause a variety of disturbances in the body. CranioSacral Therapy is a gentle way to correct those restrictions so the body can release the effects of stress naturally and heal itself.
Even the most natural of births may be stressful for the skull and spine of the baby being born. Some research strongly suggests that the birth process may be responsible for many brain dysfunctions and problems caused by central nervous system imbalances. Because CranioSacral Therapy is so gentle it can be performed at birth or within the first few days of life to potentially reduce a wide variety of newborn and childhood problems, many which are not apparent until your child is of school age. Problems of head shape, small fontenelles, and skull bone override may also be corrected with the application of CranioSacral Therapy.
Here is an article on how birth can affect babies and how Craniosacral therapy can help them
Applications of CranioSacral Therapy in Newborns and Infants, Part I | massagetoday.com