There used to be a line the MTA used - Little enough to ride for free, little enough to ride your knee. Paid passengers should have the right to have a seat when available before a child who has not paid. That child should sit on the parent's lap. If a passenger wants to give up a seat for a child, the parent should accept the seat and put the child on her lap. Caregivers can be the worst offenders. Maybe they fear losing their jobs if the kids run home and complain about not having a seat.
Our parents used to say that we are a reflection of them. It's not the children who are displaying poor manners, they really don't know any better until someone tells them. So, the next time your child wants to stand up on a piece of furniture that's not yours, tell him to have a seat. If someone offers your child a seat, you take it and give him a seat on your lap. Besides, you're the one who has to go home and do ten things before you go to bed.