Leo: Given the sentence "A woman slides down a purple water slide with a small boy on her lap into a pool." is it true that "A mother is sliding with her child."?
Mei: OK, So, let's think first...
Me:
A woman slides down a purple water slide with a small boy on her lap into a pool does not indicate that a mother is sliding with her child.
Thus, the answer is it is not possible to tell.