The only kids' show that came close was Batman The Animated Series. The Joker used "laughing gas" instead of killing people.
Frankly, it was more disturbing to see people's faces contort maniacally. They may not have intended it, but I always thought there was mental warping in addition to the physically forced laughter. The victims looked and sounded like they were going mad. Batman had a supply of "anti-toxins", and victims made full recoveries, but that part didn't stick with me.
Courage the Cowardly Dog is an outright classic, but I never thought it scary. People talk about gateway horror; Courage is gateway horror comedy. Immediately after "
R e t u r n t h e s l a b," they have Eustace being moronic or Courage spazzing out and it dispels any frightening vibes.
The fiction that really scared me as a kid was targeted at older audiences, and I was a sneaky little shit staying up to watch it. Most memorable example is the Twilight Zone episode where the doll is tormenting the kid's stepfather.
I stayed up that night brandishing a coat hanger at my toys and making threats. "I'll set you on fire if you hurt my dad." That kind of thing. Watching it now is odd. I didn't recall the stepdad having issues beyond the sadistic toy.
For those of you working through your Teletubbie trauma: