A woman and a young girl are sitting down and smiling.
A mother and daughter are chatting.
A woman and a young girl are not necessarily a mother and daughter.  Sitting down and smiling does not imply that they are chatting.
A young girl is not necessarily the woman's daughter, they could smile silently, without chatting.
Just because a woman and a young girl are sitting down and smiling does not mean they are mother and daughter.