Eustathius, on Homer, Odyssey, 11.538, 1696.40
“You should know that while Homer and many other authors say that the only child of Achilles and Deidameia was Neoptolemos, Demetrios of Ilion records that here were two, Oneiros [“dream”] and Neoptolemos.
They say that Orestes killed him in Phôkis accidentally and when he recognized that he did, he built him a tomb near Daulis. He dedicated the sword he killed him with there and then went to the “White Island”, which Lykophron calls the “foaming cliff”, and propitiated Achilles.”
ἰστέον δὲ ὅτι ῾Ομήρου καὶ τῶν πλειόνων ἕνα παῖδα λεγόντων Δηιδαμείας καὶ ᾽Αχιλλέως τὸν Νεοπτόλεμον, Δημήτριος ὁ ᾽Ιλιεὺς δύο ἱστορεῖ, ῎Ονειρόν τε καὶ Νεοπτόλεμον· ὃν ἀνελών φησιν ἐν Φωκίδι ᾽Ορέστης ἀγνοίαι, ὕστερον δὲ γνούς, τάφον αὐτῶι ἐποίησε περὶ Δαυλίδα, καὶ ἀναθεὶς τὸ ξίφος ὧι ἀνεῖλεν αὐτὸν ἀπῆλθεν εἰς τὴν Λευκὴν νῆσον, ἣν ὁ Λυκόφρων (Al. 188) ῾φαληριῶσαν σπῖλον᾽ καλεῖ, καὶ τὸν ᾽Αχιλλέα ἐξιλεώσατο.
BNJ 59 F 1b Ptolemy Chennos, Novel History, Book 3 = Photios, Bibliotheca 190, 148b21
“And [he says] that there were two children of Achilles and Deidamia, Neoptolemos and Oneiros. Oneiros was killed accidentally by Orestes in Phôkis while they fighting over erecting a tent.”
καὶ ὡς ᾽Αχιλλέως καὶ Δηιδαμίας δύο ἐγενέσθην παῖδες Νεοπτόλεμος καὶ ῎Ονειρος· καὶ ἀναιρεῖται κατ᾽ ἄγνοιαν ὑπὸ ᾽Ορέστου ἐν Φωκίδι ὁ ῎Ονειρος, περὶ σκηνοπηγίας αὐτῶι μαχεσάμενος.