I'll disagree that she had no responsibility. She recognized the
danger and returned the kid to daddy. Kid returned and she saw him
again by the water. She knew it was dangerous and should have returned
him to daddy again.
At the point she returned the child to Dad the first time, she had
already gone above and beyond any requirement to protect the child.
The fact that the Dad let the child return to the dangerous situation
puts the blame squarely on his shoulders.