This may be due to trauma, acne or rosacea. Can you elaborate more on the bumps on your son's nose? Are there other signs or symptoms present? In cases of untreated rosacea,nasal bumps, or rhinophyma, are an uncommon sign. Men are more likely to experience the small, knobby bumps on the nose. As the number of bumps increases, the nose and cheeks may appear swollen.
It would be best to have this evaluated by your doctor. A complete medical history and physical examination is needed to reach a diagnosis.
Take care and regards.