A woman in a black jacket and a black and white striped skirt is watching a woman talking to a little boy sitting on concrete steps.
A woman watches a mother speak to her young son.
Little boy  does'nt need to be her son, it may be some other boy.
The child could be anyone in the first sentence.  There is no mention of him being the woman's son.
just because they are talking don't mean she if he's mother