In the cursed child, Delphi, Albus and Scorpius travel back in time to 31 October 1981, the night James and Lily Potter were killed by Voldemort and Harry got his scar, marking the beginning of their connection. At this point, the Fidelius Charm was still active, though Peter Pettigrew had revealed the location of the family to Voldemort.
However, Albus and Scorpio can see the Potters and their house (nevermind the fact that this contradicts the letter from Lily to Serius that Harry finds in 12 Grimmauld Place where Lily writes that James is getting frustrated because they can't leave the house). Why were they able to see the house and the family even though they're protected by the Fidelius Charm? It is also never questioned that Delphi would be able to waltz in and kill young Harry, even though the Fidelius Charm was cast to prevent exactly this.
The only explanation that I can come up with is that they come from a time period where the Fidelius Charm is no longer active (since it's caster died), so it has no effect on them. But since they travelled to a time where the charm was still active, that seems rather far-fetched.