Big difference between letting kids be free to do things and not coddling them vs. using authority to push them to do things they are uncomfortable with or afraid of.
The incidents in the story, really, aren't much different from a parent pushing their kids off on their first bike ride with no training wheels. Are they going to fall? Maybe. Are they going to die? Definitely not.
Kids often have overblown senses of danger. Did the river have alligators? Maybe, maybe not (I checked though, it does), but kids are often imagining dangers that aren't there. Old Lady Crenshaw isn't really a witch, and her house isn't really haunted, and Old Man Cratchett isn't likely to shoot trespassing children on sight.
My family frequently goes to Hawaii, and while it literally took weeks to convince my child that yeah, there are sharks in the ocean, but it's still safer than the car ride TO the beach. I don't feel even slightly guilty for trading out her fear of sharks for the wonderment that is the ocean. We discussed how to deal with sharks, what to do if we encounter one, blah blah blah, but at least to me, "avoiding the whole ocean forever" was not a valid way to deal with that fear.
Do you think alligators can't kill you?
Regardless, even though you quoted out of context, it's perhaps worth backpeddling a bit, because even though I stated that they're definitely not going to die while riding a bike, even that is an overstatement. It's clearly not impossible to die on one's maiden bike ride, though it is still very, very unlikely.
Pushing a kid on a bike without training wheels for the first time could very easily be interpreted as attempted murder by a precocious child. That doesn't mean that their fears are rational. Swimming in a river has a non-zero chance of alligator attack, statistically, alligator attacks are very, very rare, and you're far more likely to die of regular old drowning than by alligator.
Crossing a road or taking a car ride is likely more dangerous.