Unless it's for consistency. If you have a long-term lie going, you need to keep it consistent, or others will notice the plot-holes.

Plain and simple

We agree. I'm saying that one is good, and the other sucks.

The way past cynical detachment is with material change, not pretense and deception.

Children may well have parents or an environment where reporting rape gets them in trouble. At least a cynical child may recognize an adult being angry at them for reporting a rape as an enemy who can hopefully be circumvented. A naive child would be blindsided and could probably be cowed into silence.

So tell them the story of Cassandra, tell them how it can really happen, and then tell them in what way they live in a society that is different from back then.

Tell them about the impulse to stay quiet and not make a fuss. Tell them about the impulse to shut down inconveniences, about gatekeepers and victim blamers and perpetrator apologists. Tell them about transformative justice, about police violence, about child protective services and its abuses. And maybe make a plan with them to find their own justice if shit were to hit the fan and the parents are unavailable/unreliable.

If it's any consolation, none of this will be nearly as daunting as them realizing they were born into a dying world and the people in charge are actively trying to make things worse.