SandraSherry,
I flew to NYC right after Sept. 11th to have my son see Dr. New. I did have a letter from my endo. I had one stop and never during my entire trip did I ever get questioned. I even had it in my hand in case they wanted to look at it and they never did. This was less than a month after Sept. 11th!!!! I think you will be fine, just have the note for "just in case".
On another note, I flew with my mon cah son when he was 6mo. old from CA to Buenos Aires, Argentina. That was a long trip. He was much younger and slept alot! My ped suggested benadryl but I didn’t use it. I would just say to keep a big bag of snacks and toys and anything you think your child would like. I once sang the itsy bitsy spider song from a CA flight to TX, just to keep my son happy!! It worked. So, get your singing voice ready!
Good luck,
Sandra