。
She took care of the children.
Literal
She [topic-は] those children [genitive-の] care [object-を] did.
世話をする ('take care of, look after') is the standard idiom for caregiving — built from 世話 ('care, attention') + を + する. The の that connects 子供たち and 世話 is the typical possessive/relational use: 'the children's care.' The phrase covers a wide range of caretaking — feeding, supervising, raising — and extends metaphorically to 'looking after a project, a pet, a job.' お世話になる ('to be in someone's care, to be indebted to') is the related polite expression for receiving such care.