As I understand it, the meanings are (always?):
...swoje dziecko – her own child
...jej dziecko – another woman's child
...her child – either of the above, depending on context:
– If woman & child are at home: unambiguous.
– If women & children are socialising around the sandbox, one might point at the person in question, or use a qualifier (...your/her child, ...Janet's child, etc.)