Must one re-fast the atonement for a child who died by drowning, and what is the ruling on a husband fondling his wife and semen being discharged during fasting if her fast is an atonement for death?

If the child's death was due to your negligence, then the expiation for accidental killing (qatl al-khata') is incumbent upon you. This expiation involves paying blood money (diyah) and freeing a believing slave. Allah Almighty says: "It is not for a believer to kill a believer except by mistake. And whoever kills a believer by mistake – then freeing a believing slave and a compensation payment presented to his family, unless they remit it as charity."

Therefore, you must pay the blood money for this child and fast for two consecutive months. The blood money is to be paid by your 'aqilah (male relatives on your father's side) and given to her heirs, unless her family pardons the blood money, in which case only the fasting remains obligatory for you. Since the freeing of a slave is not possible, fasting for two consecutive months is required. The fasting must be consecutive, and it is not permissible to interrupt it except for legitimate Shari'ah-compliant excuses. If one deliberately engages in foreplay and semen is discharged, this is considered an interruption of the continuity, and the fasting must be restarted from the beginning.