Suetonius, Aug. 4 (all Suetonius via Project Gutenberg)
After quitting Macedonia, before he could declare himself a candidate for the consulship, he died suddenly, leaving behind him a daughter, the elder Octavia, by Ancharia; and another daughter, Octavia the younger, as well as Augustus, by Atia, who was the daughter of Marcus Atius Balbus, and Julia, sister to Caius Julius Caesar. Balbus was, by the father's (73) side, of a family who were natives of Aricia 109, and many of whom had been in the senate. By the mother's side he was nearly related to Pompey the Great; and after he had borne the office of praetor, was one of the twenty commissioners appointed by the Julian law to divide the land in Campania among the people. But Mark Antony, treating with contempt Augustus's descent even by the mother's side, says that his great grand-father was of African descent, and at one time kept a perfumer's shop, and at another, a bake-house, in Aricia. And Cassius of Parma, in a letter, taxes Augustus with being the son not only of a baker, but a usurer. These are his words: "Thou art a lump of thy mother's meal, which a money-changer of Nerulum taking from the newest bake-house of Aricia, kneaded into some shape, with his hands all discoloured by the fingering of money."
... can't remember if they made anything out of this apparent connection to Pompey
Suetonius, Aug. 8
After the subjugation of Spain, while Caesar was meditating an expedition against the Dacians and Parthians, he was sent before him to Apollonia, where he applied himself to his studies; until receiving intelligence that his uncle was murdered, and that he was appointed his heir, he hesitated for some time whether he should call to his aid the legions stationed in the neighbourhood; but he abandoned the design as rash and premature. However, returning to Rome, he took possession of his inheritance, although his mother was apprehensive that such a measure might be attended with danger, and his step-father, Marcius Philippus, a man of consular rank, very earnestly dissuaded him from it.
... this stuff hasn't happened yet
Suetonius, Aug. 94
I find in the theological books of Asclepiades the Mendesian 248, that Atia, upon attending at midnight a religious solemnity in honour of Apollo, when the rest of the matrons retired home, fell asleep on her couch in the temple, and that a serpent immediately crept to her, and soon after withdrew. She awaking upon it, purified herself, as usual after the embraces of her husband; and instantly there appeared upon her body a mark in the form of a serpent, which she never after could efface, and which obliged her, during the subsequent part of her life, to decline the use of the public baths. Augustus, it was added, was born in the tenth month after, and for that reason was thought to be the son of Apollo. The (139) same Atia, before her delivery, dreamed that her bowels stretched to the stars, and expanded through the whole circuit of heaven and earth. His father Octavius, likewise, dreamt that a sun-beam issued from his wife's womb.
... hmmm ... perhaps that explains the bathing scene at the beginning (which reminded me of a scene, actually, from the recent TV version of the Odyssey)
Nicolaus of Damascus (assorted fragmenta ... all separate, not continuous as the presentation might suggest)
Octavius, at the age of about nine [twelve?] years, was an object of no little admiration to the Romans, exhibiting as he did great excellence of nature, young though he was; for he gave an oration before a large crowd and received much applause from grown men. After his grandmother's death he was brought up by his mother Atia and her husband Lucius Philippus, who was a descendant of the conquerors Philip of Macedonia.
At the time when the Civil War had laid hold on the city, his mother Atia and Philippus quietly sent Octavius off to one of his father's country places.
Caesar had by this time completed the wars in Europe, had conquered Pompey in Macedonia, had taken Egypt, had returned from Syria and the Euxine Sea, and was intending to advance in to Libya in order to put down what was left of war over there; and Octavius wanted to take the field with him in order that he night gain experience in the practice of war. But when he found that his mother Atia was opposed he said nothing by way of argument but remained at home. It was plain that Caesar, out of solicitude for them, did not wish him to take the field yet, lest he might bring on illness to a weak body through changing his mode of life and thus permanently injure his health. For this cause he took no part in the expedition.
... definitely not the Atia we saw
Octavius asked permission to go home to see his mother, and when it was granted, he set out. When he reached the Janiculan Hill near Rome, a man who claimed to be the son of Gaius Marius came with a large crowd of people to meet him. He had taken also some women who were relatives of Caesar, for he was anxious to be enrolled in the family, and they testified to his descent. He did not succeed in persuading Atia at all, nor her sister, to make any false statement concerning their family; for the families of Caesar and Marius were very close, but this young man was really no relative whatever.
It bore out the earlier news, and said that the whole populace was aroused against Brutus and Cassius and their party, and was greatly vexed at what they had done. His stepfather Philippus sent him a letter asking him not to take steps to secure Caesar's bequest but even to retain his own name because of what had happened to Caesar and to live free from politics and in safety. Octavius knew that this advice was given with kind intent, but he thought differently, as he already had his mind on great things and he was full of confidence; he therefore took upon himself the toil and danger and the enmity of men whom he did not care to please. Nor did he propose to cede to anyone a name or a rule so great as his, particularly with the state on his side and calling him to come into his father's honors; and very rightly, since both naturally and by law the office belonged to him, for he was the nearest relative and had been adopted as son by Caesar himself, and he felt that to follow the matter up and avenge his death was the proper course to pursue. This is what he thought, and he wrote and so answered Philippus though he did not succeed in convincing him. His mother Atia, when she saw the glory of fortune and the extent of the Empire devolving upon her own son, rejoiced; but on the other hand knowing that the undertaking was full of fear and danger, and having seen what had happened to her uncle Caesar, she was not very enthusiastic; so it looked as if she was between the view of her husband Philippus and that of her son. Hence she felt many cares, now anxious when she enumerated all the dangers awaiting one striving for supreme power, and now elated when she thought of the extent of that power and honor. Therefore she did not dare to dissuade her son from attempting the great deed and effecting a just requital, but still she did not venture to urge him on, because fortune seemed somewhat obscure. She permitted his use of the name Caesar and in fact was the first to assent. Octavius, having made inquiry as to what all his friends thought about this also, without delay accepted both the name and the adoption, with good fortune and favorable omen.
Cassius Dio 45 (via Lacus Curtius)
So much for Antony's conduct. Now Gaius Octavius Caepias, as the son of Caesar's niece, Attia, was named, came from Velitrae in the Volscian country; after being bereft of his father Octavius he was brought up in the house of his mother and her husband, Lucius Philippus, but on attaining maturity lived with Caesar. section 2For Caesar, being childless and basing great hopes upon him, loved and cherished him, intending to leave him as successor to his name, authority, and sovereignty. He was influenced largely by Attia's emphatic declaration that the youth had been engendered by Apollo; for while sleeping once in his temple, she said, she thought she had intercourse with a serpent, and it was this that caused her at the end of the allotted time to bear a son. section 3Before he came to the light of day she saw in a dream her entrails lifted to the heavens and spreading out over all the earth; and the same night Octavius thought that the sun rose from her womb. Hardly had the child been born when Nigidius Figulus, a senator, straightway prophesied for him absolute power. section 4This man could distinguish most accurately of his contemporaries the order of the firmament and the differences between the stars, what they accomplish when by themselves and when together, by their conjunctions and by their intervals, and for this reason had incurred the charge of practising some forbidden art. section 5He, then, on this occasion met Octavius, who on account of the birth of the child, was somewhat late in reaching the senate-house (for there happened to be a meeting of the senate that day), and upon asking him why he was late and learning the cause, he cried out, "You have begotten a master over us." At this Octavius was alarmed and wished to destroy the infant, but Nigidius restrained him, saying that it was impossible for it to suffer any such fate.
In other words, we really don't have a lot of info on Atia other than as concerns bloodlines and, if anything, there are hints that Octavius's mom might have been rather more worried about him than ambitious for him.