Apocalypse of the past

Year 2628, and the government has, inevitably, destroyed itself. Pollution has gotten so bad, scientists were forced to figure out a way to take it out of the air and place it into nuclear power plants. These power plants are placed on an island, far from the main land. This island, however, is home to the poor, disabled, and homeless. The nuclear plants can't hold the gases without expanding, creating problems. The gases have leaked from the power plants, making the island unsuitable for living. The government does not allow any evidence to be allowed to the public. A siren is played just as dusk arrives, when the tide comes in and makes the gases further expand and leak from the tanks. A family of 5 lives on the island and the only left are a daughter and the younger son. They must survive on their own and find ways to help not only themselves but the rest of the island; maybe finding their parents along the way to the mainland.