Rabbi Achai ben Yoshiyah addressed a question about the Sabbath commandment's reference to "you and your son and your daughter." Who exactly are the son and daughter mentioned here? The Mekhilta DeRabbi Yishmael records his answer: they are minors, young children who cannot yet be held responsible for their own observance.
The logic is straightforward. If the verse referred to adult children, it would be redundant. Grown sons and daughters are already obligated to keep Shabbat (the Sabbath) on their own. They have already been commanded, already exhorted. There would be no need to mention them alongside their parents.
The only reason to specify "your son and your daughter" in the context of the parent's obligation is if these children are too young to bear the commandment themselves. The verse is not telling adults to observe Shabbat. It is telling parents that their young children must also rest, and that the responsibility for ensuring this falls on the parents.
This teaching has practical legal force. A father is exhorted to keep his minor children from performing labor on Shabbat. The child is not punished for working, since a minor cannot be held legally accountable. But the parent who allows it has failed in his obligation.
Rabbi Achai's reading transforms what might seem like a simple list, "you and your son and your daughter," into a specific legal ruling about parental responsibility. Every word in the Torah carries weight, and when a word seems unnecessary, the rabbis knew it was teaching something new.