The Ark, the Reed, and the Firecloud by Jenny L. Cote
The Ark, the Reed, and the Firecloud does have some weak points, of course. Most are trivial: there are a lot of anachronisms, especially in geography, and a consistent language error in which Liz gets a masculine adjective (enchanté, malheureux) instead of a feminine one (enchantée, malheureuse). On the whole, however, there are no major problems until they're on the Ark, but the issues really pile up at the end.
1. The reed becomes more magical and talismanic over time. The first place it's a real problem is on p. 326, where Max effectively invokes the reed (not God) to perform a miracle--and a miracle God likely wouldn't have bothered with himself, considering what was actually going on. At first I thought it was a counterfeit miracle that would be acknowledged by the villain at the end. Not so: it gets worse, because the reed is the way to beat the villain (421-422).
2. The villain on the Ark is a bit of a yank anyway, but it also acts out of character. It advises Max to be open with his friends about his fears (305), though Satan generally encourages us to keep secrets like that. It apparently can be venomous (unless that's only off the Ark), yet doesn't use that to attack Noah and kin. It keeps some captive passengers alive for some reason, though being trussed up for a year without eating would likely have proved fatal to them.
3. There's a resurrection/immortality bit at the end that is a convenient plot device for a series, but it troubled me anyway.
There are other points I could mention, but these are the ones parents should be ready to discuss with the kids.
Conclusion. While the story has problems, especially toward the end, they can be useful teaching points--the parents may learn as much as the kids if they discuss the matters intelligently. So I would recommend this with reservations.