(SEE YESTERDAY'S MINCHAS CHINUCH)
On the Shita of Tosfos in Chagiga that Avadim are obligated in P'ru U'rivu, the Turei Evan asks how are they Yoitze? Their children are not Miyuches to them?
The Minchas Chinuch brings the Gemara in Sanhedrin 58b. R' Chisda says that an Eved is permitted with his daughter and mother. Since they left being a Ben Noach but hadn't yet come into the Kedusha of Klal Yisrael.
Rambam seems to learn that it's referring to an Eved who was born as an Eved and had a daughter as an Eved. Still, being in this twilight state an Eved, that's not like a Goy or a Jew that both have Yichus. This Eved doesn't have any Yichus at all .
Rashi learns that it's referring to someone born as a Goy and had a daughter as a Goy and then became an Eved. Thus, when he became an Eved he goes out of being a Goy and is not related to them anymore. But if you'll say that we should prohibit him, just like we prohibit a Ger, so people shouldn't look at it that being a Jew is inferior. If we would permit past relatives to him that was prohibited when he was a Goy, then it would seem that Goyim have more Mitzvos and thus superior. To this we say that the Eved hadn't come into the Kedusha of Yisrael yet that we should worry what people would say about him.
therefore, according to Rashi, the family that an Eved has while he's an Eved is considered his family (though Rambam would hold it's not his family) We can say that Tosfos in Chagiga agrees with Rashi and the Eved's children are considered to be his children.