For what it's worth, I survived the Salt Vampire, the neural parasites, the faceless woman on "Charlie X," and the Horta burning people to death when I was just a little kid -- and that was pretty scary stuff back then. Not to mention the scarier episodes of The Twilight Zone and The Outer Limits, as well as classic horror movies on "Nightmare Theater" and at the drive-in with my dad. Heck, by the time I was ten I was shuddering deliciously at the likes of "Count Yorga, Vampire" (the cat-eating scene!) and "Island of Terror" (bones being sucked from bodies by tentacled monsters, Peter Cushing getting his arm chopped off!).
Point being, it all depends on the kid. Some kids love monsters and scary stuff; other kids may find them too disturbing for their age. That's up to their parents to determine.
But being kid-friendly doesn't necessarily mean no scary monsters or mayhem. Heaven forbid!
(Says the sixty-five-old Monster Kid who grew up watching "Dark Shadows" as well as "Star Trek" -- and who is always kinda bemused to see the exploding alien in "Conspiracy" described as shocking and controversial.)