There are a couple of other factors in the mix. One is that you can derive Canadian citizenship, from birth, from either of your parents. You have to consider the other parent in the mix. If the other parent in the mix was born or naturalized in Canada, then the child born abroad would be a Canadian citizen through their other parent.
If that's not the case—the other parent is a foreign national with no ties to Canada—then the option for the parents, if they're wanting to return to Canada to live, is to sponsor that child for immigration to Canada.