The Story of the Treasure Seekers. by E. Nesbit

This is the story of the six Bastable children : Dora, Oswald, Dicky, Alice, Noël and little Horace Octavius, known as H. O. Due to their mother tragically passing away and their father's business partner running away with the money, the ancient and most noble House of Bastable, as the children like to call it, has fallen. In order to restore their family fortune the resourceful siblings go on a hunt for treasure ; but whether they dig for gold in the garden, or try to open up a sherry business, their treasure-hunting always ends up getting them in trouble.
The Story of the Treasure Seekers was the first novel for children written by Edith Nesbit, and today it is one of her most well-known. The stories of the Bastable children were first published between 1894 and 1899 in a variety of periodicals. For the one-volume publication in 1899 the order of the stories was changed, and several of the stories underwent extensive rewriting. This and her later novels inspired several later writers of English children's literature, amongst them C.
S. Lewis, who references the Bastable children in The Magician's Nephew. The Story of the Treasure Seekers spawned two sequels, The Wouldbegoods in 1901 and New Treasure Seekers in 1904.