It couldn't be Blue Lagoon could it? I remember there was this movie about a family that stopped at this island with their boat(suposedly in modern day times back then 80's or late 70's) and ran into a bunch of pirates that were still living like the old time pirates did. The pirates burn their boat and turn their kids into pirates while holding them prisoner or slaves. The son and daughter end up being turned into pirates too and dad and mom have to watch while plotting to escape with the family. I can't remember the name of that Movie but nobodies sold it that I know of. It was a good movie.