I found this at the library for one kid who's getting into Bigfoot, and I thought it was well done. It's one journalist's investigation into stories, evidence, and lore surrounding Sasquatch in the US. While it's not exhaustive, it's a good mix of general information and in-the-moment exploration to add a sense of adventure to the story. The author shares stories and information from Bigfoot hunters, scientists who are gathering and testing evidence, and people in neither of those categories who have had experiences they can't explain. I appreciate that some Indigenous people's stories were included too. The last chapter touches on some of the reasons why belief in Bigfoot has endured, and why so many people really want it to be out there even in the absence of scientific proof.
FYI: There is one paragraph in here (on page 120) that explains/assumes the reader knows the tooth fairy isn't real -- something to be aware of depending on the kid you're reading to/giving this to.