It wasn't the immigration officer's responsibility to notify you. It was your responsibility to do this. When you received your COPR / landing document - the letter that accompanied your COPR specifically stated that you were required to notify CIC of any changes to your family composition before landing.I got married before I landed in canada and immigration office did not inform me about informing cic about marriage. I assumed I got visa stamped before marriage therefore there is no need to inform anyone. Getting help from immigration lawyer hope is there anyway to get things right.
It's quite unlikely an immigration lawyer will be able to help you - but you can certainly try.