Thank you.
I had an almost identical case to the one you mentioned. The simplest thing to do would be to allow that individual—that child who has been accepted as a protected person—when they're applying for permanent residence, to include their parent on that application, whereby the parent would get permanent residence automatically on the basis of their child's application.
It works in the reverse. If a parent is accepted but for whatever reason a child is not, that child is that adult's dependant, so when the adult applies for permanent residence, the child gets it as well. But it doesn't work in the reverse: If the child is the protected person but the parent isn't, the parent is kind of out on their own. As you say, the logical conclusion is that the parent can be deported and we have an orphaned child who has every legal right to stay in Canada.
A simple change would be a change to the regulations that currently prevent children from including their parents in their PR applications. That's the most straightforward recommendation on that front.