I can’t imagine kids are allowed anywhere near some of these scary/spooky books we read as kids. It must have been a popular genre for kids back in the 60s & 70s. I loved scary books. And I also loved to watch the scary movies, especially the ones with Vincent Price. I was probably 7 or 8 when I first watched them. The adults never seemed to think anything of it.
The Goosebumps series?
A Series of Unfortunate Events?
Amazon even has a category for Childen’s Spine-Chilling Horror.
I’m not sure how these books compare with the books we read as children in terms of degree of scariness, but they are very popular.
Basically the first I remember, all at roughly the same time, are The Donald Duck Book, and two Dr Seuss books: And to That I Saw It on Mulberry Street, and The 500 Hats of Bartholomew Cubbins. I was maybe fours years old.
A couple of years later I had In the Days of the Dinosaurs by Roy Chapman Andrews.
My first book was a comic book, Detective Comics #179. I found it, coverless, in the attic, and kept reading it until I more or less understood the story, which was a chore since a lot of it was pretty idiotic, like a lot of the old Batmans.
A Fly Went By.
or, possibly
Nobody Listens To Andrew
The first picture book I can remember is Georgie and the Robbers by Robert Bright.
The first novel could have been The Enchanted Wood, The Wind in The Willows or The Hobbit. I have distinct memories of reading all 3 (with some help for the words I didn’t understand) but couldn’t say which was first.
When I first saw this thread, I was going to say that there’s no way I could possibly remember. But I do have a vague recollection of one of the first books I ever read myself, if perhaps not the very first, but then I was stuck on remembering the title. And it suddenly came to me – one of those very distant memories that suddenly pops up to the surface – it was It Happened One Day. The book has gone through a number of editions, but it was awesome to find this particular cover picture, because that was exactly the book I had! (I’m not quite so old that the 1938 date is pertinent – I either had quite an old book, or there were many reprints using that cover).
Now that I’ve found it, I may just end up ordering one from a used bookseller.
Ha! I found several original 1938 first editions, and just ordered one that is supposed to be in pretty good shape. Looking forward to a major burst of childhood nostalgia!
Would never have done it if the Dope hadn’t triggered this old memory! 
Carolyn Haywood was one of my favorite childhood authors. She also a series about
a character named Betsy and her little sister, Star.
Bunnicula at age 7. Made an intentional effort to emulate my parents and start reading. It worked. Being under 100 pages long was a big contributor to not getting overwhelmed.
The first book i remember reading is “Snow”. It’s in the “i can read” series, and it was boring, and my mother was teaching me to read and made me read it.
She succeeded, but i don’t remember what the first book i read on my own might have been. I do know that the first “adult” book i read was “the Lord of the Rings”. My father read “the Hobbit” to me, and i liked it, so he gave me his copy of LOTR. I was in second grade. I learned the concept of a paragraph from that book. I tried to end each night at the end of a sentence, but soon realized that some sentences weren’t good ending points. I also developed reading fluency from reading LOTR. I spent months reading “the fellowship of the ring”, but whipped through the other two much faster.
This’ll date me: I think it was a hand-me-down from my older brother, called Bulgy the Barrage Balloon
There was a book about all things underwater, both freshwater and saltwater, that belonged to my brother. It even covered diving and fishing equipment. I think the diving chapter featured Jacques Cousteau. Since I read a chapter in this book about raising brine shrimp, I was actually excited when I learned the truth about sea monkeys.