Glad you and your son enjoyed your fossil hunting trip and had success. Fife has a number of localities you can visit. Some are protected by Special Site of Scientific Interest (SSSI) status. The Scottish Fossil Code is useful to help you understand the law and rules governing fossil collecting in Scotland. Scottish Natural Heritage has a number of publications on Scotland's geology as does the British Geological Survey. This website is also useful.
In terms of books Professor Nigel Trewin's books are very good and geared to both youngsters and adults alike.
Various geological societies in Scotland organise field trips for their members. Edinburgh based Geowalks also run guided trips and have included trips to Fife.
Hope this is helpful.