I must admit that I watched "Back to the blue lagoon" over and over again when I was in the age of 20 to 30. Actually, for long time I beleived it was her own waist-length or butt-length hair, but I uppose there must have been some hair extensions covering her breasts in many scenes? She has had mid-back hair in all her other movies.
I suppose she was 14, occasionally 15, during the movie recording Chatgpt4 says that Brooke Shields has stated that she does not regret her early roles, although she acknowledges the issues surrounding them, and that she did not understand at that age. She trusted her mother, Teri Shields, who has defended her decisions and has not publicly expressed regret, even though Brooke has had mixed feelings about the impact on her life and actress carrier that the sexualized roles has had.
It was another time with another moral. Today it would not be acceptible with partly topless scenes with such a young actress, and I hope that I would not have watched it at my current age. I don't know if the full movie still is aired on regular streaming channels and TV channels, but I would be suprised if it was.