Prince
noun, suffix
The king's child is the prince. Someday he'll be the 王, if he's lucky, but right now he's just the king's child, a.k.a. the prince!
If you prefer some grammatical details, you can try to remember that when a word consists of two kanji, sometimes the first kanji has a possessive relation to the second. In this case, 王 possesses 子, making it the king's child. Historically, male children had priority in royal succession, so I guess that's why this word means "prince."
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. Also take note that the reading for 子 (し) is changed to じ.
That said, this reading can be easy to confuse with other similar words, so here's a mnemonic to help you out:
The prince is always saying "Ohh, Jesus (おうじ), please let me be king!" In fact, the prince probably says "Ohh, Jesus" to ask for help at least once a day.
王子が「おはよう！」いってくれた。
The prince said "Good morning!" to me.
王子は小さいころに子犬をかってた。
The prince had a puppy when he was little.
うちの子は王子にハグしてもらいたい、と天にいのってばかりよ。
My child constantly prays to heaven for a hug from the prince.