Linda Blair. But there should definitely be an option for Quinn Lord who played Sam from Trick 'r Treat. He did a fantastic job!
Corey Haim in THE LOST BOYS I think his is the only lead character in the list. Though I could be wrong.
Well, the thing is Danny didn't even know he was doing a horror movie. A lot of his performance was assembled from what Kubrick was able to do with him. Danny never knew context. It's hard to gauge a performance that way. Linda Blair was excellent in The Exorcist, I'm especially thinking of the medical experiments which chilled me more than anything else the film has. Her reactions were not stock, like even the possessions were, but had a realistic tone that would seem to come from knowledge beyond her age. I'm sure she had excellent direction, but still it was talent on her part.
WHAT A LIST! I had to give it to Heather O'Rourke, because she was so damn cute! But, after that- the honorable mentions go to Felissa Rose, Courtney Gains, Kirsten Dunst, and Linda Blair. None of which naturally could do "uh huh... uh uh" like Heather.