Two children have nasal polyps

My two kids (8 and 6) both have nasal polyps. I only discovered them because they were constantly picking at them and told me they felt something was there. I phoned the doctor and he said ‘it’s highly unlikely to be nasal polyps in children’ but confirmed it is (in both nostrils for my eldest and one nostril for my youngest). He gave us a steroid to use for 2 months but it hasn’t worked to shrink them.

Should I be concerned? I don’t want them to have surgery. The youngest suffers from post-nasal drip and the eldest has hay fever.