Hi agree with the PP. They can skin test young children. My DD (no cf) was skin tested at 26 months and started allergy shots a month later. RAST testing is a blood test. Also, does your DS, or has he ever had reflux?? We found out my DS had silent reflux that was contributing to his sinus problems. His sinuses are still bad but we've been able to avoid another surgery with the combo of allergy & reflux meds, nasal steroids, allergy shots, and nasal rinses.