Okay kiddo, so you know how sometimes you make new friends at school or in your neighborhood? Well, in music there's also something called "new kids" or "new bands".
Sometimes, bands or groups of people come together to make music for the first time. They might be made up of people who were already famous and successful on their own, or they might be completely new to the scene.
When we say "new kids on the blecch", it's kind of like a funny way of saying "new kids on the block", which means new people who are joining an established group or community.
So, when we say "new kids on the blecch", we're talking about new bands or musical groups that are coming onto the music scene and trying to make a name for themselves. They might have different styles of music, different looks or personalities, and they'll be working hard to get people to notice them and listen to their music.
It can be exciting to discover new music and see these new kids grow and succeed in their careers. But, like with anything new, it can also take some time for people to get used to them and decide if they really like their music.