if the visa you are talking about is for pr, as soon as the baby is born, the visa office must be notified, and the baby must be added to the application, or else, the baby will be excluded from future sponsorship to Canada.
if the visa is for visiting, again, as soon as the baby is born, you either need to apply for a visitor's visa for the baby or add them to your daughter's current application so the baby can come to Canada as a visitor. i'm sure senior members will confirm which is needed for a newborn's visitor's visa.
if the baby is not born before LANDING as a pr or traveling as a visitor, then there is no need to contact the visa office. if your daughter is applying for pr and gives birth AFTER landing, then she must go through the process of sponsoring the child to remain in Canada as a pr.