Midrash su Salmi 22:32

It was taught: From what age has a minor a share in the world to come? R. Chiya and R. Simon b. Rabbi differ. According to one, immediately after birth, and according to the other, from the time he commences to speak. The former infers it from (Ps. 22, 32) Will tell his righteousness to a people just born, and the latter infers it from the foregoing passage, Zera (children) shall serve him; there shall be related of the Lord unto future generations. It was taught: Rabina said: "From the time he is formed"; and R. Nachman b. Isaac said: "From the time he is circumcised, as it is written (Ps. 88, 16) I am inflicted and perishing from my youth up." There is a Baraitha in the name of R. Mair: "From the time he can answer Amen, as it is said (Is. 26, 2) Open ye the gates, that the righteous nation that keepeth faithfulness (Shomer Emunim) may enter in." Do not read Emunim (faithfulness) but read it Amen. (Fol. 111) What does Amen mean? It is an abbreviation of El melech N'eman, God, King of Truth.