I'm not sure which tpye of flight/plane it was (i've only ever flown twice before on very low budget flights!), but by "somewhere more quiet and with more space", i meant perhaps another part of the plane that wasn't so crowded? Maybe an area where staff have access that wasn't being used all the time? It might have been okay for the boy and his mum to go in there for a breather?
I'm just trying to think, what adaptations can actually be made on flights for people with neurodevelopmental disorders. Obviously, everybody is entitled to travel. But this little boy is obviously highly distressed by it. What could be put in place to make his next flight feel more comfortable for him and, as a result, more comfortable for his mum and other passengers?
Increased awareness of neurodevelopmental disorders might be a good start!