L'arbre de Noël

Since the death of his mother, Pascal, ten years old, spends his holidays with his father, the rich Laurent Segur. One day, when diving near the shores of Corse, an aircraft falls into the sea. The holiday goes on happily with Catherine, the young and pretty girlfriend of Laurent. But soon blue marks appear on the face of Pascal. He has been contaminated by a nuclear weapon carried by the destroyed plane, and he won't survive more than six months. There is nothing Laurent can do, except give his son the best six months he has ever lived. - IMDb