legs radical (no. 10)
儿 is a radical form representing human legs. Its standalone meaning is limited to this radical sense, used as a component in other characters.
儿 is a pictograph of two human legs, derived from the lower part of the character 人 (person). It serves as a radical in characters related to legs or human posture.
The two strokes look like a pair of legs walking: 儿 is the legs radical.
For ジン, imagine a pair of jeans (ジーンズ) walking on two legs: jeans -> ジン, and the legs radical 儿 wears them.