If by "Worst" you mean annoying or posessing horrible acting skills then I would have to mention that little bastard from 'The House by the Cemetary'. He bugged the living s**t out of me!
Yes, evil kids is where I was going with that one. I think the boy in the original Omen was disturbing,but that was a long long time ago. He freaked me out when I was a kid.
If by worst you mean evil, then I would have to go with the scaple totting, achilles cutting, living dead little bugger from Pet Semetary. He was creepy!
I will have to admit that is the funniest response ever. Ya, nanny shows do count!!!!!........ there are alot of little HELLIONS out there every day.....I should know I have two of them at home... HAHA