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.
Minor Issues:
-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