子 pictures a swaddled infant with a large head and outstretched arms. Oracle bone forms emphasize the disproportionate baby head — the same observation modern parents make. Identical across 繁體 / 新字体 / 简体.

The character has three distinct life-modes you must learn separately:

1. As a content word: child / son / offspring. 子女 (zǐnǚ / shijo, sons and daughters), 王子 (wángzǐ / ōji, prince), 弟子 (dìzǐ / deshi, disciple), 君子 (jūnzǐ, gentleman in Confucian sense), 孔子 (Kǒngzǐ, Confucius — "Master Kong").

2. As a noun suffix in Mandarin (this is where Japanese learners get tripped up). Modern Mandarin attaches 子 (pronounced lightly, neutral tone "zi") to many nouns to mark them as concrete objects: 桌子 (zhuōzi, table), 椅子 (yǐzi, chair), 孩子 (háizi, child), 房子 (fángzi, house), 包子 (bāozi, steamed bun), 鼻子 (bízi, nose). This pattern does NOT exist in Japanese or Korean — it is a Mandarin-specific grammatical particle that happens to use this character.

3. As a Japanese girl-name suffix. The kun-reading こ (ko) finishes a huge percentage of traditional Japanese feminine names: 花子 (Hanako), 良子 (Yoshiko), 智子 (Tomoko), 順子 (Junko). Modern naming has moved away from the pattern, but it remains classically feminine.

Mandarin: zǐ, dipping 3rd tone (when content word); neutral when suffix. Japanese on-reading シ (shi) in 弟子 (deshi, disciple), 男子 (danshi, male), 女子 (joshi, female).

Memory aid: a baby with arms out, head big — bundled in a blanket.