This is from Stalin's Daughter by Rosemary Sullivan:
Nadya left Svetlana's nanny strict instructions never to let her charge be idle. Svetlana remembered her nanny taking her to preschool for music lessons with twenty other children. Svetlana sang in a children's chorus and was soon taught to read and transcribe music and play the piano.
I think 'her' indicates Svetlana's nanny, if so what is the meaning of 'charge' here? Is it 'an assigned duty' or 'one that is entrusted to another's care'?