Sorry I can't really say.
Being in Canada is a requirement for the oath ceremony, and the kid doesn't need to be in the oath ceremony, so being in Canada shouldn't be a requirement and I don't think it will be problematic, but no idea how it goes if the kid's PR card isn't available.
Is IRCC fine with the kid joining from outside the country to cut it, or a picture of a cut PR card sent by mail? Maybe, but dunno how it will actually go.
If there's no time to send the card via UPS, Fedex or whatever, show up at the oath ceremony and see how it goes...
Let us know please.
Good luck !