Plato, Laws 790c

πρὶν ἂν καὶ τὰ περὶ τὰς ψυχὰς τῶν πάνυ νέων παίδων ἐπιτηδεύματα ἀποδῶμεν κατὰ τὸν αὐτὸν τρόπον ὅνπερ ἤργμεθα τῶν περὶ τὰ σώματα μύθων λεχθέντων διαπεραίνειν. πάνυ μὲν οὖν ὀρθῶς. λάβωμεν τοίνυν τοῦτο οἷον στοιχεῖον ἐπʼ ἀμφότερα, σώματός τε καὶ ψυχῆς τῶν πάνυ νέων τὴν τιθήνησιν καὶ κίνησιν γιγνομένην ὅτι μάλιστα διὰ πάσης τε νυκτὸς καὶ ἡμέρας, ὡς ἔστι σύμφορος ἅπασι μέν, οὐχ ἥκιστα δὲ τοῖς ὅτι νεωτάτοισι, καὶ οἰκεῖν, εἰ δυνατὸν ἦν, οἷον ἀεὶ πλέοντας·

of young children in the same manner as we commenced our advice regarding their bodies. You are quite right. Let us take this, then, as a fundamental assumption in both cases,—that for both body and soul of the very young a process of nursing and moving, that is as continuous as possible both by day and by night, is in all cases salutary, and especially in the case of the youngest: it is like having them always rocked—