In Islam, parents are supposed to be good models for their sons and daughters. The mother is required by Islam to dress modestly in front of her son, especially when he attains the age of puberty.
Sheikh Ahmad Kutty, a senior lecturer and Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada states: “In the presence of grown children who has attained the age of puberty, you can dress modestly as you would normally do at home. More precisely, your attire must cover your body, both front and back, to your knees – including your breasts.
In other words, you are not required to cover your hair, face, shoulders, neck, arms, and legs below the knees in front of your son as well as men who are directly related to you in blood relationships and whom you cannot marry. What I have said above is the generally accepted view of scholars and is duly supported by evidence from the Qur’an and the Sunnah.
Having said this, we must add that the above rule applies in all normal circumstances. However, in the case of any suspicion of evil intent or fitnah, one is required to take that factor into account and, thus, cover appropriately.”