CHILDREN OF THE BLOOD is a supplement to CULTS OF THE BLOOD GODS and a stretch goal for its Kickstarter. Basically, it is a book of NPCs (or SPCs as White Wolf is now styling its terminology) as well as some rules for running cults in the World of Darkness. It is a spiritual successor to CHILDREN OF THE INQUISITION, which was a book that provided some important power players like Dracula and Etrius during the early days of the line. It actually reminds me a bit more of CHILDREN OF THE REVOLUTION in that it is a bit less overt in the importance of the NPCs that it presents.
There's a little more than twenty NPCs in the book with a mixture of the good, the okay, and the excellent. Rather than focus on the most terrifying and powerful of the undead world, it mostly includes mid-tier NPCs that are a mixture of Neonates and Ancilla. There's only a handful of Elders present among their ranks and they tend to be very distinctive. I prefer this as 5th Edition has done an excellent job of ratcheting down the power level of encounters so that PCs have a chance of shooting or talking their way out of encounters.
I admit to a certain level of bias with Oscar Vasquez a.k.a "The Operator", Faith Corrigan, and Misery among the NPCs since I contributed Kickstarter-based "pitches" for them. They've been since written up by professional game developers and improved significantly from my rough ideas. Still, I loved seeing them in print so any review reader should be aware. They're a psychopathic assassin from before their Embrace with the latter giving them feelings they didn't have in life, a Church of Caine Anarch spreading her gospel, and an early Gothic Punk band leader turned political genius.
There's a lot of really interesting and good ideas spread among the characters with many of them being the sorts that could liven up an existing campaign or provide the basis for an adventure or two. Interesting characters include "Doctor Starr" who is regularly the meat puppet of an ancient Malkavian, Belinde Buch the Prince of Copenhagen who looks like a human doll, and Florian Ribiero who is an aggressive mathematical perfectionist that can't reconcile the supernatural to his Spinoza-esque worldview.
Perhaps the most interesting character in the book is Father Christian Patriot. An obvious parody of your typical Qanon conspiracy theorist, Father Christian Patriot is a Thin Blooded vampire who basically has his weekly rants uploaded by his followers. He's an interesting character as his sire never thought to teach him about the Masquerade so he's just flat out not bothered with it. I found it interesting that in a game about blood-drinking, murder, seduction, torture, and inner darkness that his bigoted beliefs are enough to get a warning sidebar. I don't disagree with it, quite the opposite, but find it amusing since the text is clear that he's a complete moron.
You're probably not going to be able to squeeze all of these people into your campaign or even a third of them but there's plenty of potential plot hooks to draw from as well as interesting, well, NPCs. The book has a mild tie to LET THE STREETS RUN RED as well with the characters of Akawa, Anastasia, and Freddie Montgomery from the Chronicle "Innocence in Blood" being given full write-ups here. I always appreciate expanding on past characters with Akawa and Anastasia being originally detailed in Milwaukee by Night way back in 1st Edition. I would also love to see Freddie encounter Father Christian Patriot since she was raised by a similar cult. It might be an eye opener.
Gameplay-wise, this is not a heavy crunch book. The book "technically" introduces two new Bloodlines via Loresheet with the Milliners and Rosselinis but that's stretching my definition of Bloodline with the two Giovanni families. We also got some more Loresheets with the standout ones being the One True Way and Menele worshiping cult. I found the latter a little strange given I don't recall any Menele-worshiping NPCs in the book. On the other hand, I appreciate the detail put into the One True Way in this book as a "False Golconda" cult that is objectively just driving Kindred closer to wassail is a fantastic idea.
There are also rules for the various kinds of cults you can run and coteries that can emerge from trying to manage your own Kindred religion. One of these coteries indicates that Marcus Vitel a.k.a Lucius Sejanus is building his own religion about himself and that just makes sense. There's a good number of merits and flaws for the Cults of the Blood God religions as well that will appeal to those who like those sorts of things too. Possessing ancient tomes, being excommunicated from your faith, and other good storytelling ideas.
In conclusion, this is an excellent albeit optional supplement to get. Onyx Path Publishing is doing a lot of the heavy lifting in continuing to crank out supplements for Fifth Edition when other publishers are failing to meet demand. It's also helping set the tone for the line with things like Chicago by Night and Cults of the Blood Gods showing us how "5th Edition in action" works. Really, the books pick up a lot from where Beckett's Jyhad Diary left off and define the setting even more than the official "main" supplements do for me. The painted artwork is also superior to the photograph of the main book, IMHO, too. You'll be able to play without this book but I feel your gameworld will be enriched by it if you get it.