What does a possessive phrase contain?

When writing a possessive phrase, you add an apostrophe and an "s". You add the apostrophe first.
TRUE OR FALSE?

Why does the apostrophe come before the "s" in children's?

Which one is correct?
The classes' timetables were all full.
The class'es timetables were all full.

Which is correct?
here are some do's and don'ts
here are some dos and don'ts

"the newspaper's readers" is an example of a plural possessive phrase.
TRUE OR FALSE

Is the statement below correctly punctuated?
London's population is one of the most ethnically diverse on earth with more than 50 non-indigenous communities.