knee-high to a grasshopper

Adjective

idiomatic not-comparable

(idiomatic) short; especially relating to when the subject was a small child

Japanese Meaning

幼少期に非常に小柄であった、つまり子供の時の身長が著しく低かったという比喩表現 / 比喩的に「小さかった」や「幼かった」といった意味合いを表す表現

She was knee-high to a grasshopper when she first started working in the garden, but now she's an expert.

彼女が庭仕事を始めた頃はひざ丈ほどの背丈だったが、今では達人だ。

Sense（1）

(idiomatic) short; especially relating to when the subject was a small child