My granddaughter likes the American Girl books.
I always loved Nancy Drew mysteries (and the Hardy boys).
My sister loved the Anne of Green Gables books.
My favorite book as a small child was “Little Black Sambo”. Our library (and many others)pulled it from the shelves because they deemed it “racist”. How ridiculous! It was wonderfully fun make believe about a little Indian boy with pointed shoes and pretty new clothes. He was not a black African person at all.
You can find most anything on the web. My son downloaded every Sherlock Holmes mystery (one per night) until he read them all. Many can be found on the Gutenberg project. Others can be found with a Google search.
These two series originated with the Stratemeyer Syndicate, which was based on South Orange, New Jersey, but which has since moved on to better digs. Edward Stratemeyer wrote the plot outlines but hired anonymous ghost writers to actually write the books under various house names. In 1977 Canadian author Leslie McFarlane wrote The Ghost of the Hardy Boys, a story of how he ghost-wrote most of the first 26 books that comprised the series. It's one of the funniest books I've ever read.
By the early Sixties, the syndicate had a new generation of ghost writers rewrite the originals with a less literary content to match a less literary readership. The originals from the Twenties and Thirties are available from boutique publishers.