וְלִמַּדְתֶּ֥ם אֹתָ֛ם אֶת־בְּנֵיכֶ֖ם לְדַבֵּ֣ר בָּ֑ם בְּשִׁבְתְּךָ֤ בְּבֵיתֶ֙ךָ֙ וּבְלֶכְתְּךָ֣ בַדֶּ֔רֶךְ וּֽבְשָׁכְבְּךָ֖ וּבְקוּמֶֽךָ׃
A nauczajcie ich synów waszych, mówiąc o nich, gdy siędziesz w domu twoim, i gdy pójdziesz drogą, i gdy położysz się, i gdy wstaniesz;
Rashi
לדבר בם [AND YE SHALL TEACH THEM UNTO YOUR CHILDREN,] TO SPEAK OF THEM — From the moment when your son knows how to speak, teach him the text (Deuteronomy 33:4) “Moses commanded us the Torah as a possession of the congregation of Jacob” — so that this should be the means of teaching him to speak (Sukkah 42a). From this they (the Rabbis) derived their teaching: When the babe begins to speak, his father should speak with him in the Holy Tongue, and should instruct him in the Torah. If he does not do this, it is as though he buries him, as it is said here, “And ye shall teach them unto your children to speak of them, etc.”,
Sforno
ולמדתם אותם את בניכם, train your children in the regular performance of the commandments
Rabbeinu Bahya
ולמדתם אותם את בניכם לדבר בם, “You shall teach them to your children to speak about them.” From the time your son (or daughter) is old enough to talk you must instruct him in Torah. One of the first lessons should be the verse תורה צוה לנו משה, as well as שמע ישראל .