Well I am a teen so I am one of the "kids" today if you mean minors. All I know about the previous generations of kids is what I see in T.V. shows, movies, video games, books, etc. So from what I can tell, I guess that in some regards kids today are nicer and in some regards kids back then were nicer.
I don't think kids today are as sadistic as some kids used to be. I mean when was the last time anyone saw a high school prank or one kid just deciding to assault another kid? I certainly don't think that bullies exist today in the same way they are portrayed to have been 10 years ago.
That being said, I don't think that kids these days do everything better than kids back then. While I don't know many kids who are straight up malicious or cruel, I don't know many who are as heroic as most of them make themselves out to be.
Overall, I just think that the reason why kids today seem nicer is because they have more empathy, but when it comes to manners, dedication, and values, I think this generation is worse.