No I do remember Timm saying somewhere that the WB wanted Superman to be lighter and more kid-friendly. But it's been so long I can't remember where I saw it.
Well, I just recently rewatched the series, and if they'd wanted it to be "kid-friendly," they wouldn't have allowed so much blood and death in it. Seriously -- in all of the FOX run of B:TAS, you saw Batman bleed maybe once or twice, if even that, but in S:TAS, Superman -- yes, Superman -- bled on several occasions. And in B:TAS, they couldn't show death or even talk about it openly. Depictions of the murder of Bruce's parents always had to be indirect and vague and symbolic. But S:TAS opened with the destruction of an entire planet and the death of everyone on it. And later in "Little Girl Lost," when Superman discovered Supergirl in cryogenic suspension, the frozen corpses of her mother and the others in her family were shown on camera, something FOX would never have allowed in a million years.
The show that WB wanted to be more kid-friendly was Batman Beyond, as I recall. Though despite the teen hero and the prevalence of stories about students, teachers, parents of students, school counselors, etc. turning into supervillains, it ended up being just about the darkest DCAU show up to that time, with a lot more villains dying at the end.