The ages aren't quite right, but is this your Christina Nicholson with Malcolm, 19, and John, 13, in the 1881 census? They're living at Queens, P.E.I., Lot 60, and Christina is a widow. There are images of baptism cards for quite a few children of a John and Christina (Christy, Christiana, etc, sometimes with surname McLean) in the Baptism Card Index for P.E.I. at LDS FamilySearch. Go to the home page, scroll down and on the left side you'll see "All Records Collection" and "Browse by Location"...this will lead you to the P.E.I. browsable records. I'm attaching the image of the card for Malcom.