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.