Passage 10.25.7
οὗτοι μὲν δὴ ἀνωτέρω τῆς Ἑλένης εἰσὶν ἐν τῇ γραφῇ· ἐφεξῆς δὲ τῇ Ἑλένῃ μήτηρ τε ἡ Θησέως ἐν χρῷ κεκαρμένη καὶ παίδων τῶν Θησέως Δημοφῶν ἐστι φροντίζων, ὅσα γε ἀπὸ τοῦ σχήματος, εἰ ἀνασώσασθαί οἱ τὴν Αἴθραν ἐνέσται. Ἀργεῖοι δὲ καὶ ἐκ τῆς Σίνιδος θυγατρὸς γενέσθαι Θησεῖ Μελάνιππον λέγουσι, καὶ ὡς ἀνέλοιτο ὁ Μελάνιππος δρόμου νίκην, ὅτε οἱ Ἐπίγονοι καλούμενοι Νέμεια δεύτεροι οὗτοι ἔθεσαν μετὰ Ἄδραστον.
These figures, then, are painted above Helen. Next beside Helen is the mother of Theseus, depicted with close-cropped hair, and Demophon, one of the sons of Theseus, who appears deep in thought, at least judging by his posture, considering whether or not it might be possible to rescue Aethra. The Argives relate that Theseus had a son named Melanippus by the daughter of Sinis; and they recount that Melanippus was victorious in the footrace at the games established by the Epigoni, the second Nemean Games, first instituted by Adrastus.