If your kid's temporary residence status is expiring along with your WP, then they also needs stay extension(Visitor Record extension).You need to apply for your WP + Spouse OWP + Kid's Visitor extension together in a single online application.
If any of the applicant(s) have arrived in Canada less than a year and not done Canadian medical examination in last one year , then they may need medical and proof of medical receipt shall be included in the online application. There are some more conditions as well , please check with CIC about your case, Careful here, they will reject your application without asking you , if the medical is needed in your application and if you fail to provide.
TRV is optional , Needed only if you want go out of Canada and re enter, TRV is to be obtained from CIC-Ottawa. You required valid WP/Visitor record to obtain it .TRV will be issued up to your WP/Visitor record validity.
