Adopted Child
noun
If you foster a child for long enough, eventually you'll want to adopt them and make them your adopted child.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
駅長の子は、どうやら養子らしいです。
I heard that the station master's kid is actually an adopted child.
私の友人は、赤ちゃんを養子に出すことにしました。
My friend decided to give her baby up for adoption.
二人は養子をもらって育てました。
The couple adopted and raised a child.