Can a brother and sister take bath together and saw each other's body?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

It is not permissible for a brother and sister who are adult to bath together in a way that one could see the 'Awrah (parts of the body that should be covered in Islam) of the other, as the Prophet said: "Conceal your 'Awrah except from your wife and from what your right hand possess.'' [Ahmad & Abu Daawood].

Therefore, it is not permissible for a man to reveal his 'Awrah to other than his wife. Similarly, a wife is not permitted to reveal her body to anyone other than her husband. Also, it is not permissible for the guardian of these young children to allow them to bath together if they have reached the age of distinction.

For more benefit on the 'Awrah of a woman in front of her Mahaarim (i.e. plural of Mahram, who is a spouse or a person whom one is permanently prohibited from marrying due to suckling, marital, or blood relations), please refer to Fatwa 90591.

Finally, it should be mentioned that if the brother and sister are below the age of distinction, like being two years old, then it is permissible for them to be uncovered in front of each other and bath together.

For more benefit, please refer to Fatwa 85134.

Allaah Knows best.