One of my most heart rendering moments in life was watching a mother with a downs syndrome kid being escorted off a plan because he "would not settle".
Selfish people were complaining because he was crying an upset. He was sat in his seat, but clearly very upset.
I was ashamed of everyone on that plane who complained, and when I saw the poor mum's face my I died a little inside. That poor lady was just trying to take a flight home with her disabled child, and just because people were not happy with a bit of noise on public transport they had to suffer further.
Parents do not want to upset people on the plane. Trust me, they already feel terrible if their child is crying and causing scene, they don't need people with total lack of empathy and patience making their nightmare any worse.
Just suck it up, put on a smile and put on your headphones. You are an adult with the freedom to travel unhindered, if you can't deal with an upset child for a few hours, then how will you ever cope with life?
I have not flown with my kids yet (6 and 3) but some people have to fly with kids as it's the only practical way, just give them some space and know that you can get off the plane and saunter off into your perfect life with little consequence from your "ordeal".
However, if you are on short haul and you EVER recline your seat (or even on long haul without at least notifying the person behind you first) you deserve to die