When I was s child, little ones travelled free, and under 14s at half price. Now children pay full fare (not sure about toddlers). Over 60s travelled free, and now people have to wait until they are 67.
When there were so many concessionary fares, drivers (or conductors, back in the day) could insist on people giving up seats as a condition of the concession. There were signs to that effect on the buses.
Now, people are paying full fare (expensive where I live - £8 to the city from my hometown) and often see no reason to give up their seat. There are more older-but-not-old-enough-to-go-free people who might need a seat, and of course there are people of all ages with hidden disabilities.
Who is entitled to a seat, and who ‘should’ give theirs up is always going to be a judgement call.
I do feel that if people are using passes they should be considerate about travelling at peak times. Commuters are likely to be tired after a full day at work, and buses are full anyway. When lots of seats are taken by older shoppers with lots of bags, it perhaps makes commuters less likely to want to give up a seat. Travelling off peak would make having a seat of your own more likely anyway, and free up a space for those with no choice.
A mother standing when her toddler sits is teaching consideration, rather than entitlement, IMO. The stronger person stands, and the weaker sits. I would have put mine on my lap, true, but there may have been a reason why this wouldn’t work for that mother and child.
I think we should be less ready to judge one another. We don’t always know what is happening in others’ lives.