Inevitable
Necessary, Foregone
な adjective, の adjective
If it's certain that you will attain it, then it is inevitable. It is a foregone conclusion.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
子どもへの性教育はある時期では必至になると思うんですが、日本はそうした教育については通常どのように行われるんですか。
I think it’s necessary to teach kids sex education at some point, but how do people usually teach those things in Japan?