I cant remember the name of a movie?

i don't remember much about it because i haven't seen it since i was like 8 years old. what i do remember is there were some lost kids floating around in some old ship or something. there is a scene where a mermaid pops out of a huge oyster. i think the movie is from the 90's or 80's. i know this isn't a lot of details but any ideas would be very appreciated