As a mother, in the presence of your son you are required to dress as you would normally do so at home. That means that you are not required to cover your hair, face, shoulders, neck, arms, and legs from below the knees in front of him.
Sheikh Ahmad Kutty, a senior lecturer and Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states: In the presence of your son who has attained puberty, you are required to dress as you would normally do so at home. More precisely, you must cover your body to your knees – both front and back (including your breasts). In other words, you are not required to cover your hair, face, shoulders, neck, arms, and legs from below the knees in front of your son as well as any men with whom you have direct blood-relationships and hence cannot marry. What I have said above is the generally accepted view of scholars and is supported with evidence from the Qur’an and Sunnah.
Having said this, we must add a further note: the above rule applies in all normal circumstances. However, in the case of any suspicion of fitnah (sedition), one is required to take such factors into account and, thus cover as appropriately as the situation requires.