Our son has been on it many times - starting when he was 2. We told him that the ghosts were funny and he went with that. Wasn't really old enough to understand why it could be scary other than the dark. Since then he has really grown to enjoy it. Last week he insisted on riding it (he's 3 1/2 now) and was actually put out by the hitchhikers - thought they were rude since it was "our car". Loved everything else.
One thing...when we took him on it the first time, I was positive I had scarred his little psyche for life. He stared, motionless and took it all in. I was panicked since he wouldn't look at me or respond to me when I talked to him...just took it all in, wide eyed. Then when we got off, he started talking non stop and wanted to ride it again. WHEW! Since then, I've realized that's just how he enjoys that ride...just absorbing it all.