yīng / ér / qī / shì / hái / zi / shēn / tǐ / hé / dà / nǎo / kuài / sù / fā / zhǎn / de / jiē / duàn

婴儿期是孩子身体和大脑快速发展的阶段。

Infancy is a period when a child's body and brain develop rapidly.