When shows first begin, they usually have a period where everything's new and rough and the characters and plotlines are still trying to sort themselves out. Then eventually all the pieces start coming together and the show gains a solid loyal audience and becomes the show we know today. That's what we mean by established.
Yes. There were things that really seemed ironed out by the 72 season. And by 1974/75 they pretty much had a formula they used up until 2002. So, as I said earlier, episodes from 1969-1971 may raise a kid's eyebrows, but anything after that period is perfectly fine.
Personally, I always wondered this. Until recently, kids all grew up on Looney Tunes and older shows with no real complaints. Even now, kids are still watching old Scooby-Doos (as they have been since the late 90's). Other than some relaunches on the part of Scooby-Doo with movies (both live action and DTV animated versions) and a couple cartoons (the first series being an upgrade of the older series, the second being their odd change of pace that comes up every so often), there hasn't been anything that really changed his views in the public eye, especially with children. Looney tunes, I could go onto a rant about. Long story short, WB doesn't give a crud, and they don't know what they're doing outside of DVD releases. But even still, if kids aren't swayed by the older animation style of Scooby Doo (with the exception of Laff-a-lympics and 13 ghosts, I believe all the shows aired on CN for a time- and some on Kid's WB), who's to say that kids automatically like new anyway.
Outside of the group of smaller kids whom Elmo's World cannot be removed for, I see no problem with most of the stuff on both SSOS DVD sets. And didn't they release quite a bit of older material on the 30 minute DVD's as well (though We are All Monsters was redubbed with Kevin Clash doing "yet to be determined red monster's" voice). Even today, there are things from even the 70's that would fit perfectly. I bring up yet again the Checker playing Bernice skit.