Indeed, we would like to differentiate between two main points:
1-Fending off aggression launched against Muslims: This should be done without transgressing the limits laid down by the Qur'an. Allah Almighty says: "Fight in the cause of God those who fight you, but do not transgress limits for God loveth not transgressors." (Al-Baqarah: 190)
2-Giving regard to the Islamic war ethics: It has not been recorded along the course of Islamic history that Muslims raped women of their enemies or even killed their children. Hence, the point referred to here in your question (i.e. raping enemies' women) is not allowed in Islam and it is not the manners of Muslims. Though many rape incidents have been recorded, where Muslim women were brutalized by enemies, there is no single record of such incident taken place among Muslims, even as a war retaliatory measures.
Confirming these facts, we would like to cite for you the Prophet's instructions to his chief commanders while dispatching them to resist aggressions: "Fight in the Cause of Allah. Fight those who deny Allah; Do not be embittered. Do not be treacherous. Do not mutilate. Do not kill children or those (people) in convents."
Here is Abu-Bakr's instructions to Usama while embarking on the Levant Campaign:
"Do not betray or be treacherous or vindictive. Do not mutilate. Do not kill children, the aged or women. Do not cut or burn palm trees or fruitful trees. Don't slay sheep, cows or camels except for food. And you will come across people who confined themselves to worship in hermitages. Leave them alone to what they devoted themselves for."
Focusing more on the question in point, Sheikh Ikrimah Sabri, The Mufti of Al-Quds (Jerusalem) & Khatib of Al-Aqsa Mosque, states:
"In fact, the principle of reciprocity has well-established rules in Shariah, whereby Muslims are warned from embarking on such inhumane attitudes. For instance, in case the enemy mutilates the dead bodies of Muslims, the Muslim army is not permitted to act in the same manner."
Based on this, it is not permissible for Muslims to rape female captives under the notion of reciprocity. There is nothing like that in Islam. However, if the enemy kills Muslim captives, we are permitted to kill their captives in retaliation.
In all cases, Muslims should not initiate the aggression, for Islam is the religion of mercy. War is not the first option in the life of Muslims; rather, it comes after dawah (proselytizing) and kind advice.