So I heard this from a friend. This is only a theory.
Since the kids are on an island with memorials of themselves, there is a possibility of the entire cast not being the actual people themselves but actually clones. With the technology of being able to bring back extinct animals, they probably could also create clones of the deceased people using their DNA.
Also, the mother spoke about the island being a paradise, but since the cast is "dead", it could mean that they were planning on cloning the victims on the island in the first place. The scientists hoped to make it paradise but with their death and the help of the "terrorists", the extinct animals were able to escape into the wild. =
This theory also has a lot of holes (the plane, age, etc.), but it is a pretty satisfying theory in my opinion.