Sometimes the younger kids are less afraid than the older kids. I think it may be that the older kids have a more developed imagination or something.
With my own kids, I noticed they did things when they were young with no fear. But then around 3 or 4 years old, things that used to never bother them (heights on the playground) scared them. I noticed it with a few of my kids. They didn't fall or anything. They just got older and got scared on the high places.
So, I can understand why a kid of 3, 4, 5, or 6 would be scared by the ride while younger kids are not. The younger kids don't know enough yet to be scared.... I guess.
Very true. I've always read that it's because a younger kid feels they are invincible - there's that whole body of research about how toddlers will do dangerous things without getting scared. They don't have true sense of danger, a true concept of what death is, or that they can get hurt. So when they are on a ride, they don't get that the monsters/ghosts/etc. in the ride are dangerous. If they're scared it's usually because of loud noises, motion or something that is new to them. Whereas an older kid understands those concepts, and can be frightened by them.
We've been going to the parks regularly for years and years. Each of our kids made their first trip at 10 days. Our son's first trip on pirates was at about 4 weeks. He sat on my husband's lap and slept through the whole thing. Our daughter went on pirates at 10 days and she too slept through it. When she was really little I'd take her on it just so she'd have a bit of a nap while we were in the parks. They've always been fine with it. You can see just how little she was in my avatar. That picture is from her first trip. Occasionally they'll say they don't want to ride something but I think it has more to do with their moods than anything else. Just take your cues from your toddler. You know them better than anyone else.
I say...it depends on the kid. My daughter's first trip to WDW was when she was 3. She loved POTC and HM. HM became one of her favorites, even at that young age. When we went back 2 years later for the Halloween party...she wanted to dress as the tightrope walker. She STILL loves both rides and it's 7 yrs later. It really depends on the kid. I've seen kids in there older than her that scream at everything.
Little tip....if you act like it's no big deal...odds are..they will too. If you laugh and giggle..they probably will do. Toddlers feed off of your reactions.