II was just watching this on youtube ( there are 20, 10 minute segments of the whole movie, the appearance I saw was on part 17 at about 7min 30 seconds he runs in) He is the grandson of the movie star character played by John Carradine, father of Kieth, David and Robert) When they are being rescued, he runs up with an older woman , his grandmother. I believe John calls him "Kevin"(gee imagine a mistake in a movie) but one look at that kid, it's Kirk probably about 8-10 years old if that.

I have the longer version and the only time i see him is at the end when the passengers are putting on scuba gear. He is with an older woman comforting her about putting on the gear.