As a young girl growing up in the 70s, I was never allowed to watch anything even resembling a horror movie, but sometimes Satan's minions find their way onto pre-school programs. When I was growing up, the queen of horror had to be Lady Elaine Fairchilde from Mister Rogers' Neighborhood. Of all the weird things I remember seeing on Sesame Street during the 70s, the one that really stuck with me was the freaky, opera-singing orange.
While my children were in their Nick Jr. years, I always found the slurms from Eureka's Castle to be decidedly creepy (see Night Of The Creeps or Shivers to get an idea).