John Calvin Commentary Numbers 30:1

"And Moses spake unto the heads of the tribes of the children of Israel, saying, This is the thing which Jehovah hath commanded." — Numbers 30:1 (ASV)

And Moses spoke. Moses teaches in this chapter that vows made by persons who were not free were not considered valid before God. Although no mention is made of male children, still, since their condition was the same, it seems that by synecdoche, they must be included with the daughters and wives, unless perhaps God chose to show particular regard for women.

But since He permits women, who were not under their father’s authority, to make vows despite their gender, nor does He allow this to be an excuse for frivolity or thoughtlessness, it seems that the proposed objective was that the authority of the father over his children, as well as that of the husband over his wife, should be kept inviolate.