Betsy and Tacy Go Downtown by Maud Hart Lovelace

Betsy, Tacy, and Tib are twelve—old enough to do lots of things...even go downtown on their own. There they see their first horseless carriage, discover the joys of the public library, and see a real play at the Opera House. They even find themselves acting in one! Best of all, they help a lonely new friend feel at home in Deep Valley—the most wonderful place in the world to grow up. Ever since their first publication in the 1940s, the Betsy-Tacy stories have been loved by each generation of young readers.