Your children visa will expire when your medical expires! So, it is advisable to land together. Also you should arrange where to receive the PR cards in Canada which takes around 45 days to be sent to you. You require a valid PR card or a valid Permanent Resident Travel Document (PRTD) to re-enter Canada by commercial carrier.
If you gave Immigration, Refugees and Citizenship Canada (IRCC) an address in Canada, but you left before the card was mailed to you, you can ask your family or friends who live at that address to send you the PR card. You can then re-enter Canada with your PR Card.
If you have arrived and have not yet given IRCC a mailing address, and you left Canada, you should apply for a Travel Document (Permanent Resident Abroad) before you try to re-enter Canada. This application must be submitted to a Canadian visa office abroad.
This Travel Document can only be used once. You are not guaranteed to get the Travel Document, if you apply. It is up to the officer at the visa office to decide if you will get it or not. For further details visit here
http://www.cic.gc.ca/english/information/applications/travel.asp