According to Talmud scholars:
According to rabbinical tradition Daniel was of royal descent; and his fate, together with that of his three friends, Hananiah, Mishael, and Azariah, was foretold by the prophet Isaiah to King Hezekiah in these words, "and they shall be eunuchs in the palace of the king of Babylon".Isaiah 39:7 (Talmud tractate Sanhedrin 93b; Pirke de Rabbi Eliezer lii).[1]
According to this view, Daniel and his friends were eunuchs, and were consequently able to prove the groundlessness of charges of immorality brought against them, which had almost caused their death at the hands of the king. It was said of Daniel, "If he were in one scale of the balance and all the wise men of the heathens in the other, he would outweigh them all" (see Yoma 77a).[1]
Nebuchadnezzar admired Daniel greatly, although the latter refused the proffered divine honors, thus distinguishing himself favorably from his contemporary Hiram (the "prince of Tyre" Ezekiel 28), who demanded honor as a god (Genesis Rabba xcvi.).[1]
http://en.wikipedia.org/wiki/Daniel_in_ ... literature
Daniel was a major prophet in the old tradition and when the Talmud was written down, the scholars of the time refused to write all the oral tradition about Daniel onto papyrus (or whatever passed for paper). Angels are not mentioned or named in the Book of Danil in the Talmud but they are in the Christian texts. So the two accounts differ.
The "Eunuch" idea comes into the texts in chapter one - -
3 partial: Then the king said to Ashpenaz, his chief officer, to bring from the Children of Israel, from the royal seed, and from the nobles.
4: Youths in whom there is no blemish, of handsome appearance, who understand all wisdom, [who are] erudite in knowledge, who understand how to express their thoughts, and who have strength to stand in the king's palace, and to teach them the script and the language of the Chaldeans.
5: The king allotted them a daily portion of the king's food and of the wine that he drank, and to train them for three years, and at the end thereof, they would stand before the king.
6: Now there were among them, from the Judahites, Daniel, Hananiah, Mishael, and Azariah.
http://www.chabad.org/library/bible_cdo ... pter-1.htm
And in the KJV, the names are Daniel, Shadrach, Meshack, and Abednego.
Ashpenaz is King Nebuchadnezzar's chief of staff (my words) and a Eunuch. So It is assumed that all the "boys" were made Eunuchs.
That to me is pretty thin evidence. I'm not Jewish. If someone else can read the Talmud and the Rabbinical commentaries for more information, please do.