It would have been interesting to explore characters as they age throughout the show. Given the shows longevity it could have been really interesting to have a varied set of characters age right along with the viewers.
Children could identify with Elmo for their entire lives. The Elmo of today would be finishing school and starting a job, and only visiting occasionally. He would take a very different role than that of 20 years ago.
The point is, Maria and Gordon __have__ been with the show for decades, and now their characters have kids. Similarly, some of the kids in earlier years still are involved as older kids. It's one thing I have really liked about the show, as it lets them show nuanced relationships (both in terms of jobs and family).
But they have. And to agree with both you and the parent post, watching with my child the other day, I noticed an adult actor that looked familiar. I looked it up, and he had originally been one of the child actors when I was watching as a kid.
Granted he wasn't anywhere near as frequent as the puppet characters, but still amazing.
Children could identify with Elmo for their entire lives. The Elmo of today would be finishing school and starting a job, and only visiting occasionally. He would take a very different role than that of 20 years ago.