Hi,
You have received citizenship certificates for your kids without attending the virtual oath because as per immigration laws kids under 14 don't require to attend the ceremonies and their citizenship certificates are being sent by mail and that is the norms. You need just to send a proof that you have invalidated their PR cards by cutting them. The norms also being the parent, you need to go to the passport office and submit the passport applications for your kids and eventually you as the parent can either receive them in person or by mail, Back to your specifics, what you need to do is to return to Canada (I believe you are a Canadian citizen yourself) apply for your kids passports, receive them then fly back to where your kids are and now your kids can enter the country as Canadian citizens with their newly issued passports. Your kids can't enter Canada anymore with their PR because the PR's in your hand right now are invalid and your kids are no more permanent residence but Canadian citizens.
