links18 said:
Were such children's citizenship retroactive to birth?
Yes, the children of Canadian-born parents were given citizenship retroactive to their date of birth OR January 1, 1947, whichever is the more recent date. What has caused some confusion, though, is the thought that if the person was a citizen from birth, then they must have been a citizen when their children were born abroad, and that those children should also now be citizens. The reason this isn't the case is that the limitation on citizenship to the 1st generation born abroad went into effect at the same time (April 17, 2009) as the children of Canadian-born parents received their retroactive citizenship. So, only if a person was a Canadian citizen before April 17, 2009 did they have the potential to pass their citizenship on to their children born in the 2nd or subsequent generation.
Just to reiterate: with very few exceptions (diplomats, formal renunciations*) anyone with a parent born in Canada is, as of the citizenship changes of 2009 and 2015, a Canadian citizen.
*swearing an oath to the USA and renouncing foreign potentates is NOT a formal renunciation.