This is the 413th most frequent Japanese word.
子
"子" means "child" or "offspring" in English.
Here, '子' (こ, ko) is a prefix meaning 'child' and is combined with '猫' (ねこ, neko), meaning 'cat', to form '子猫' (こねこ, koneko), meaning 'kitten' or 'young cat'.
子猫が公園で遊んでいます。
A kitten is playing in the park.
In this sentence, '子' (こ, ko) is used as a standalone noun meaning 'child', referring generically to a young person.
舞台に立ちたい子はいますか？
Is there a child who wants to stand on the stage?
In this sentence, '子' (こ, ko) is used as part of the word '子供' (こども, kodomo), which means 'child'. It refers to someone's offspring or young person.