formal a baby or very young child.——朗文当代大辞典

 A child during the earliest period of life (or still unborn); now most usually applied to a child in arms, a babe; but often extended to include any child under seven years of age (cf. infant class, infant-school n.); in early use (esp. when transl. Latin infāns, or French enfant) used in the wider sense of ‘child’, and thus passing into the legal sense——牛津当代大辞典  @en