My kids are not reading by themselves yet but we have read them the Rainbow Fairy books, a bunch of Judy Moody books, a few Junie B Jones and are about to start a Clementine book. I always hear people talking about the Magic Tree House books.
DS has read a Magic Tree house book, and a Junie B Jones Book, but I can tell , while he loves it when we read them to him, he was bored reading it himself, He loves reading books that have lots of of pictures, so right now he's reading the Fly Guy series, and the Bad Kitty Series by himself.
DS isn't reading by himself, but the first chapter book I read him was The Mouse and the Motorcycle. We've read almost all of the Magic Treehouse books and are starting on the Captain Underpants books.
Re: What is the first chapter book your kid read
DD: Catwings, by Ursula LeGuin or Magic Tree House
DS: Bad Kitty Takes A Bath, by Nick Bruehl or Magic Tree House
Magic Tree House
But they have been replaced with a growing collection of Captain Underpants...I am so proud.