Is there a sin upon the parents of the girl who drowned in the pool, given that there were means of prevention and the incident occurred in a moment of inattentiveness?

The ruling regarding the drowning of the child depends on knowing the causes of the drowning and the surrounding circumstances. If someone caused the drowning due to negligence or dereliction in her care, then expiation (kaffarah) and blood money (diyah) are incumbent upon him, payable to her 'aqilah (male relatives responsible for paying blood money), unless they pardon it. An example of negligence is allowing someone who cannot swim well to swim in a dangerous place, or neglecting to supervise someone who requires supervision. If the negligence was of this type, then the person entrusted with the child's care must pay expiation (fasting for two consecutive months) and blood money to the remaining heirs of the child, unless they pardon it. However, if the negligence was ordinary and customarily excusable, then neither expiation nor blood money is obligatory.