Interesting to see I'm not the only one who's complained about this.
I don't think it's the kids, though - I don't remember who does Herry, but most of the really memorable kid segments were done by either Jim Henson or Frank Oz as one of their many characters, and they both have a special sense of how to talk to kids that I think is lacking in current SS (I think Kevin Clash is one of the better ones, though)
A prime example is the payoff for today's JTE: Ernie (Steve Whitmeier) introduces a kindergartener with a rubber ducky collection. He first introduces the child, then asks all kinds of questions, and basically ignores the answers. When the kid tries to engage Ernie by asking him to add his rubber ducky to the collection, the response is a kind of panicked giggle.
It seems the days when Muppets talk to kids like they're people with something important to say are gone. It does take a special combination of listening, ad libbing, and directing which is a real loss for SS.