Said fact is that if you forbid something with no more explanation than "I said so", people can't help but be curious about it. If you tell someone not to think about the purple elephant or they'll be punished, they're going to be thinking about that violet pachyderm because you called it to their attention. It's as simple as that. Well, maybe not so simple when you're dealing with a simpleton parent like Elly. She and John fret and stew about how terrible it is that their children will be exposed to dangerous information because, well, they only trust their children to make the most destructive choices because they're afraid of them and they can't articulate what it is that bothers them without Elly having to face up to the fact that the real reason that sex terrifies her is that it releases tension and forces her to confront the dangerous fact that most of the bullshit she worries about is just that.
The reason that this is a problem is that Elly thinks that the constraints that should bind everyone else should never have been applied to her as a child. This leads us to having her bleat to companion inept numbskull parent Connie about how unfair it is that her children are curious because she wants them to not be while at the same time complaining about how unfair it was that her own parents set any limits on her own behaviour. This is called boomer lens-cap stupidity.