Hi!
So with a free account, you are unable to generate pairing codes for your parents, that's a paid account admin feature only.
What you need to do with a free account is have the students go on their canvas account, click the 'Account' button on the global navigation bar (the bar on the left side of the screen) then click Settings. After that, over to the right of their screen should be a button called Pair With Observer. Once they click that, a code will generate for the parent. The parent has to download the Canvas Parent app on their phone, create an account, then add that pairing code that the student has provided to them.
Students must be in a course with a STUDENT role in order for the pair with observer button to appear in their settings.
Hope this helps, please reach out with any questions.
Noah