Are they angels?
children of the "judges"?
[Note Onkelos has a third read - viz. children of the "powerful"]
It turns out that Rabbi Shimon Bar Yochai comes out on both sides of the dispute!
First, See Torah Temimah on B'reisheet 6:2 Ot 2
The TT quotes Yoma 66b re: "Azazeil" etc. and the Rashi on that passage, which favours the first defintion, and then TT says it is "mashma m'forash b'Zohar"
However, B'reisheet Rabba on THIS Passuq quotes RaSHbY that
«B'nei Elohim elu b'nei dayyana» and that RaSHbY would curse anyone who would say they were angels [B'nei Elohaya]
This contradiction is noted by the TT himself.
The TT supports the read of the Talmud and Zohar from Avot d'Rabbi Nathan ch. 31 that mentions a grave sin was a LACK of judges during that era.
This conclusion may be somewhat disputed by Onkelos' definition above that they were neither children of Judges nor angels, but children of the "mighty"