So after my wife and me did medicals in early September and updated children information to the application in late August with all other updates, we were expecting medical request for kids soon after.
Instead, we got RPRF request for the two of us a month after, which (as much as happy we were) scared me that maybe they missed to include the kids in further visa processing.
Almost 2 months after RPRF request and 3 months after children documents/other forms and PCC update was done, the kids finally got the invitation for medical exam.
I guess every time additional family member is being included in the application it takes a while to process it. Some immigration consultants say that although kids don't have to submit PCC, their names still go through the system screening, as there are number of things that can prevent the kids from being able to leave their native country (social service issues, custody, etc.....).
The medical exam has now been completed, and with RPRF previously paid, now we have to wait for medical results and final decision and hope it's going to be positive with COPR.