KKOB, My daughter has the sunflower lanyard and all the UK airlines and airports we have used recognise it, not so much abroad.
We book special assistant (mainly for my mother who has physical disabilities) but also for my daughter, I just point it out to them at the desk but you can book special assistance just for special needs, i think it comes under the umbrella of intellectual development or something similar.
We have found the airlines to be generally compassionate towards her needs, which is mainly anxiety based around crowds.