For the safety of both the adult and the child, Canadian Aviation Regulations require that no person shall be responsible for more than one infant (children under the age of two).
As time is of the essence during an evacuation, it is very difficult to safely evacuate an aircraft in a timely manner while holding two or more infants. The aisle and row width as well as the dimensions of the emergency exit openings are the two major factors that inhibit a rapid egress.