1) How old is your mattress?
2) Do you have a box spring
3) What type of pillow do you use, age, how many?
4) Have you had whiplash?
If your bed is old, it will have a major effect on posture. The type and number of pillows also will have an effect. Sleeping on your back or fetal position can help. Do NOT sleep on your stomach.
Then the type if treatment or method of treatment. There are many chiropractic techniques. It is best to have a thorough conversation with your Doctor of Chiropractic to what therapeutic approach he/she would use.
The main suggestion I would offer is that you are seeing a chiropractor who has experience with children. Ask first then treat. You did not state why he was being adjusted. Children under regular chiropractic care are healthier, get sick less often and get well quicker if they are sick.