And before anyone comments - in my days as a child, children were expected to stand to allow adults to sit when there were insufficient seats - my how the world has changed.
As a parent (with kids ages 7 and 9), I partly agree with you, but it does depend on the distance travelled etc. On a bus or tube train or short crowded commuter train, I would expect my kids to stand (or sit on my knee). But on an
HST▸ "Intercity" Journey of 3 hours, I would want us all sat around a table and would make seat reservations to ensure this.