。
She was worried about her children's future.
Literal
She [topic-は] children [genitive-の] future [subject-が] was-worrying.
Another classic example of the ~が心配 frame: the experiencer (彼女) is the topic, and the worry-trigger (子供たちの将来) takes が. English flips the relation to '[she] was worried about [the future],' but Japanese treats the future itself as the grammatical subject of the worry. Concern over a child's 将来 ('future, prospects') is a perennial Japanese parenting concern, often inflected by educational milestones, career path, and marriage prospects.