I suspect kids in China would care about 1989 like kids in the USA in 1989 cared about the Kent state massacre: not very much, it was a long time ago right? But then that begs the question why the CPC bothers to censor it, perhaps they just don’t want to chance an open discussion about it since many of those people are still alive.
You have to remember that the people on HN from China or Chinese is not representative of the average person in China. My cousin was born and raised in China in a tier 2 city. He now works in a tier 2 city making 30K RMB/month which is extremely good pay. He has travelled abroad many times and reads western books/culture.
I was born in China and left at 16. Educated in Canada and went back at 26 and worked for 14 years there before I left. When I was there I was working in major IT companies in a tier 1 city.
You have to think about Hu's The Harmonious Society Idea (https://en.wikipedia.org/wiki/Harmonious_Society) and part of the 'Stability At All Cost' ideal. The censorship is for the average person in China.
Kent state and Tiannamen are hardly comparable.
Tiannamen could have ballooned into a full on revolution, there were many killed, imprisoned indefinitely with arbitrary trials, hurt, families threatened, careers stomped out etc..
To add:
Kent State was a spontaneous situation, violence broke out at a student sit in, with thousands of students potentially overwhelming a small number of state troopers, some of whom foolishly shot into the crowd.
Fundamentally not comparable.
I don't think that is the only view about what happened at Kent State, but it is really beside my point.