Is it obligatory to feed ten poor people for every oath sworn, or from the time one becomes aware of the obligation to feed them, knowing that the oaths were sworn previously?

Oaths must be upheld, as Allah Almighty says: [And guard your oaths]. The aforementioned oath is considered a conditional oath, contingent on the girls going out and playing. If this happens, and there was no intention to contradict the apparent meaning of the oath, then you have broken your oath and are liable for expiation. The expiation is: feeding ten poor persons, or clothing them, or freeing a slave. If one cannot find these, then fasting for three days. Fasting is only permissible when unable to perform the first three options.