When you teach your son, you teach your son’s son.

The Talmud (AD 200-500) Collection of Jewish rabbinical writings
Seder Nashim, Kiddushin 30a

Paraphrase of "This serves to say to you that whoever teaches his son Torah, the verse ascribes him credit as though he taught him, and his son, and his son’s son, until the end of all generations" (alt. trans. "to him who teaches his son Torah, the Writ ascribes merit as though he had taught him, his son and his son's son until the end of all time!"). This is in turn referenced to Deut. 4:9.