My sense is that he was known to frequent PBS viewers (I remember him from before 2010) — but the whole Chia-fro thing and "happy clouds" or whatever meme-like thing that comes to mind definitely took him to the mainstream crowd with the internet.
Sesame Street, Mr. Rogers, Reading Rainbow, Joy of Painting, Arthur, Bill Nye, Barney, Teletubbies, etc.
It's not like there were a lot of TV choices for kids if their parents couldn't afford cable (and some stations like Cartoon Network didn't even exist until 1992+, I think even Disney Channel was a premium channel like HBO).