http://www.cic.gc.ca/english/citizen/howto-e.html

Applying for children (citizenship)

If you are the parent of a child who is under 18 years of age, you may apply for your child's citizenship as soon as the child receives permanent resident status. Children do not need to have lived in Canada for three years to become citizens. To apply for your child, you must already be a Canadian citizen yourself or you must be applying to become a citizen at the same time.

Children do not have to write the citizenship test.