I showed my two videos of all the rides they were tall enough for a few weeks before the trip. They were super excited for all of them. (3 years, 4 months)
BTMRR: Huge hit, they loved it, and asked to go on over and over
Splash Mt: LIked the ride, but also did not like getting soaked, only rode once
Space Mt: Only went once on the first day, and weren't too sure about a do-over. Until we walked past it the second day and they demanded a few more rides!
Star Tours: Only went once, but that was a time issue. They talked about that ride a lot, and now want to see Star Wars (which I think they're too young for LOL )
ToT: Went once, and once was enough for them
I never asked if they were scared, in fact never even used the word. I didn't want to set up the expecation that it might be scary. I just showed them all the videos so they were familier with the rides. Then, once we were on, they could remember what parts came next.