Rashi on Exodus 20:10/רש"י על שמות כ׳:י׳

1אתה ובנך ובתך THOU AND THY SON AND THY DAUGHTER — these latter mean the young children. Or perhaps this is not so, but it means your adult children? But you must admit that these have already been placed under this prohibition (by the word “Thou”, because the performance of this command is obligatory upon all adults to whom it was addressed). Therefore these words must be intended only to admonish the adults (implied in the term “Thou”) about the Sabbath rest of their young children (to impose upon the parents the obligation of enforcing the Sabbath rest upon them) (Mekhilta). This is the meaning of what we have learnt in a Mishna, (Shabbat 16:6) “A minor who is about to extinguish a fire — we do not listen to him (do not permit him to do this), because his observance of the Sabbath is a duty imposed upon you”.