My son was born premature and had x-rays while he was in the nicu. when he was 3 he also had 2 ct scans of his head (6 months apart) because of a head injury. is his risk of getting cancer increases?

The diagnostic studies are unlikely to increase his cancer to any measurable degree. You may assist him in developing healthy habits that would reduce his risk, e.g. no alcohol, no tobacco or street drugs, get HPV vaccine, avoid excessive exposure to sun, have a mostly vegetarian diet and exercise regularly. Drink enough water so urine is mostly colorless. Wish you and you son good health!