This is a 5e one-shot adventure/mini-setting written by a father and 6-year-old son team, and I would strongly recommend it on that setup alone.
You play as creatures called Lovies. These are imagined beings that belong to (and defend) a particular child. There's a bit of neat meta here, where they don't have a religion from the 5e books---their religion is the child---and it's little details like this, both sweet and unexpectedly powerful, that I think are the strongest argument for grabbing a copy of the book.
Other noteworthy features include a built-in hideout (the Couch Dungeon,) a Ryutama-style GMPC who can swoop in if things get truly dire, my favorite giant crab in gaming, a wartorn playscape where dinosaurs are your friends and the undead are not, and a bestiary including a laser chainsaw tyrannosaurus.
Although it's designed for 5e, BB also seems quite playable with other, lighter systems such as Threadbare, so if 5e is a disqualifier for you, it may still be worth giving it a look.
Overall, if you like 5e or want a flavorful setting about children's toys fighting nightmares, or if you want an rpg you can run for a young audience that likes crunch, there's a lot of content in here.
If you're not looking for a game that's themed around children and toys, or if you're not interested in 5e and don't have anything you'd prefer to run this with, this may not be your thing.
-Page 5, the "This game provides some alternate rules" paragraph is repeated from page 2
-There's no table of contents. It's a 28 page document, so a toc may not be super necessary, but there are two pages explaining where everything in the book is, so a toc could replace that with something in a format much easier to skim.
-Page 7, "Your child" this is a heading, and 'child' feels a little weird uncapitalized