I've been trying to find this film for years now, can't really remember a lot about it just that its about 2 boys who are on a school trip and they run away and get on a boat or raft and paddle to an island where they meet a convict (maybe 2) and they try and hide from him, and I remember a little cabin where they hide out at on the island. Can anyone help me?

It sounds like "Adventures of Tom Sawyer". Much the same scenario. Raft, two boys, river, convict, cabin...