How do you or OP know whether something like this was or wasn't said to the child?
The examples I'm thinking of is places like doctors waiting rooms, trains and train stations, buses, airports, places where everyone sit and wait and you get plenty of time to observe from the time the family comes in the vicinity.
I don't automatically make an assumption because indeed, you never 100% know and I would certainly never say anything, but there are certain characteristics you notice, and yes, I have felt quite sorry for the children who seem to get so little attention and their behaviour seem to reflect it.
Children need to learn to think rather than express a stream of consciousness verbally And to learn to think, they need stimulation.
A train, library and cafe are not places to work, indeed, libraries have places that encourage interactions and places to work quietly. Once again, it's not about kids being able to be loud and the centre of attention, it's kids needing interaction to learn.