baby monkey
Refers specifically to a young, infant monkey.
動物園で子猿が母親にしがみついていた。
At the zoo, a baby monkey was clinging to its mother.
small monkey
Refers to a monkey of small size, not necessarily an infant. Can overlap with 'baby monkey' in casual use.
この種類の小猿は手のひらに乗るくらい小さい。
This kind of small monkey is so tiny it can fit in the palm of your hand.
Standard kanji spelling for 'baby monkey' or 'small monkey'.
Alternate kanji spelling; 小 emphasizes smallness.
Mixed katakana-kanji spelling, sometimes used for emphasis or in children's materials.
Rare spelling using 仔 (young animal).
Mixed kana-kanji spelling, common in informal writing.
Compound of 子 (こ, 'child') or 小 (こ, 'small') + 猿 (さる, 'monkey'). The reading こざる is a straightforward combination.