The House of Arden - E. Nesbit

This novel describes how Edred and Elfrida Arden and their Aunt Edith embark on a treasure hunt through time - for the famous Arden family treasure. With help from the magical creature Mouldiwarp, they find a whole lot of excitement and adventure. They need to discover the missing fortune before Edred's tenth birthday - or it will never be theirs. (Summary by Neeru Iyer)