Faithful
Devoted, Loyal
な adjective
I have loyalty to you, so I always tell you the truth. I am very faithful and devoted to you!
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
私達の子どもはあなたの子と違って、忠実に言うことを聞くんです。
Our kids faithfully do what they’re told, unlike yours.