This book has the exact same plot as Five on a Treasure Island, give or take some details. It's a simplistic story about a group of children and their dog determined to find the lost treasure of whatever to help their family. There are the obligatory adult caretakers who don't really understand what the children are doing and so almost stop them from succeeding. There are the lower class, but very friendly and proper farm adults who exist to feed, serve and believe the children. There are the 'bad' adults, trying to buy the property and get the treasure themselves. Naturally the children win.
It's a light read that's quite fun, but nothing out of the ordinary.