Why were the time travellers able to see and interact with the Potters?

Question

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The only explanation that I can come up with is that they come from a time period where the Fidelius Charm is no longer active (since it's caster died), so it has no effect on them.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.

Answer 1

The heart of this contradiction is Harry's assertion that the charm must have been broken because of his parent's death.

‘Look … look at it, Hermione …’
‘I don’t … oh!’
He could see it; the Fidelius Charm must have died with James and Lily. The hedge had grown wild in the sixteen years since Hagrid had taken Harry from the rubble that lay scattered amongst the waist-high grass.

_{^{Harry Potter and the Deathly Hallows — CHAPTER SEVENTEEN — Bathilda’s Secret}}

However, the fact that young Albus and Scorpius (and others) can see the property would strongly suggest that Peter Pettigrew's betrayal of their secret resulted in the spell being canceled entirely.

Note that Harry is quite open about his ignorance on the subject

He was not even sure whether he would be able to see the cottage at all; he did not know what happened when the subjects of a Fidelius Charm died. Then the little lane along which they were walking curved to the left and the heart of the village, a small square, was revealed to them.

_{^{Harry Potter and the Deathly Hallows — CHAPTER SIXTEEN — Godric's Hollow}}

and that the more people who know the secret, the less powerful is the spell. Potentially Voldemort and Pettigrew could have simply told hundreds of Death-Eaters the location, reducing the spell's efficacy to nearly zero.

‘And as there are around twenty of us, that greatly dilutes the power of the Fidelius Charm. Twenty times as many opportunities for the Death Eaters to get the secret out of somebody. We can’t expect it to hold much longer.’

_{^{Harry Potter and the Deathly Hallows — CHAPTER SIX — The Ghoul in Pyjamas}}

Note also that the narrator describes the spell as broken, not merely abated.

And along a new and darker street he moved, and now his destination was in sight at last, the Fidelius Charm broken, though they did not know it yet … and he made less noise than the dead leaves slithering along the pavement as he drew level with the dark hedge, and stared over it …

_{^{Harry Potter and the Deathly Hallows — CHAPTER SEVENTEEN — Bathilda’s Secret}}