Plato, Laws 664c

ἀληθέστατα ἐροῦμεν ἅμα, καὶ μᾶλλον πείσομεν οὓς δεῖ πείθειν ἢ ἐὰν ἄλλως πως φθεγγώμεθα λέγοντες. συγχωρητέον ἃ λέγεις. πρῶτον μὲν τοίνυν ὁ Μουσῶν χορὸς ὁ παιδικὸς ὀρθότατʼ ἂν εἰσίοι πρῶτος τὰ τοιαῦτα εἰς τὸ μέσον ᾀσόμενος ἁπάσῃ σπουδῇ καὶ ὅλῃ τῇ πόλει, δεύτερος δὲ ὁ μέχρι τριάκοντα ἐτῶν, τόν τε Παιᾶνα ἐπικαλούμενος μάρτυρα τῶν λεγομένων ἀληθείας πέρι καὶ τοῖς νέοις ἵλεων μετὰ πειθοῦς

but we shall also convince those who need convincing more forcibly than we could by any other assertion. We must assent to what you say. First, then, the right order of procedure will be for the Muses’ choir of children to come forward first to sing these things with the utmost vigor and before the whole city; second will come the choir of those under thirty, invoking Apollo Paian as witness of the truth of what is said, and praying him of grace to persuade the youth.