مناسك حج - مكارم شيرازى، ناصر - الصفحة ٥٨ - Process of Ihram
at the noon of the day of Arafa during Ihram of Hajj, and at the time of seeing Kaba in Umrah al- Mufradah( if the pilgrim has gone out of Mecca for Ihram, and if he/ she is coming to Mecca from out of the city stops saying Labbayk when he/ she is entering the region of Haram ).
Article ٧٢- A mute pilgrim points with his/ her hand instead of saying" Labbayk" and moves his/ her tongue as normal and it is better that another person says Labbayk in behalf of that pilgrim, but it is not obligatory.
Article ٧٣- Children also can become Muhrim for Umrah or Hajj, and if they discern between good and evil they can say" Labbayk" with the intention( Niyyah ), and if they do not discern a person makes intention and says Labbayk in behalf of then and whenever a person is unconscious in Miqat it is possible to make intention and say Labbayk in behalf of him/ her.