Charles Ellicott Commentary Exodus 2:4

"And his sister stood afar off, to know what would be done to him." — Exodus 2:4 (ASV)

His sister: Presumably Miriam, the only sister of Moses mentioned elsewhere (Exodus 15:20–21; Numbers 26:59). To have taken the part assigned to her in this chapter, she must have been a girl of about fourteen or fifteen years of age, and possessed much quickness and intelligence.