This post seems to me to be the heart of the issue:
"We went to a large event in a city recently, transport was enormously busy. My mother was with us, she is in her 80s and walks with a stick yet on the train heading home two boys, I'm guessing around 10 and 12, who were sitting with a couple who looked to be in their late 50s or early 60s remained sitting while she struggled to hold onto a rail and her walking stick. A middle aged woman near them gave mum her seat and said very loudly and pointedly that she should not be standing as it wasn't safe for her and that she was giving up her seat as the boys hadn't seen fit to and yet they and the adults with them still sat and ignored her.
I do sometimes wonder how society will be in the future when children are brought up with such a lack of consideration for others"
I don't think anyone would disagree with the need for others to give up their seat for your elderly DM, CalmYoBadSelf. But surely the point is, every seated bugger on the train who was able to should have been jumping to their feet and offering their seat to her? If anything, the children are less culpable, not more culpable, because they do not know better. All the adults could reasonably be expected to know better, because irrespective of how they were brought up, they are adults and can be expected to think for themselves. Plus, standing on a very crowded train is clearly a bigger deal for a child than it is for an adult. Handles at wrong height, being swayed around. It's obviously manageable, but it's easier for people in their 20s, 30s and 40s to manage than for 10 or 12 year olds.
So while it's clear that the children ought to have stood up, it's even clearer - at least to me - that the able-bodied adults really really ought to have stood up, and they should be the main targets of your dismay and anger, not the kids.