This is a book I borrowed from the library at school in approx 1970.  I remember the title as The Treasure Seekers, or something like that, but it is not the classic by E Nesbitt, and also I may be completely wrong about the title!   The story, as I remember it, involved a family of children who lived with their mother in a big old house, they were facing financial ruin, and there was an evil landlord (or similar) who was threatening them with eviction.  The children get wind of a rumour of hidden treasure, and the story follows their attempts to find the treasure in the house and grounds.  I am not sure of any of these details, but the one thing I remember clearly was that the plot came to a climax when they found a missing clue pasted to the walls of the dolls’ house in the nursery.  This is one of the earliest books I can remember reading independently and the sense of being completely gripped by the developing story contributed to my life-long love of reading.  I would love to find out what the book was, and perhaps share it with some of the children in my life now to see if it stood the test of time.