Commentary for Kiddushin 137:2

If we have a verse that teaches that in all cases where the woman cannot be betrothed to an Israelite, the children follow the mother, then what do we need the verse from Exodus for? Why have a specific midrash when we have a general one?
The answer is that the verse from Exodus can be used for another midrash. A master tries to free a female slave but tells her that her future children will be his. According to R. Yose the Galilean, this does not work. Once she goes free, her kids are hers. However, the sages say the offspring belong to the master even after the mother is freed.
The verse quoted seems like it should explain the position of the rabbis. And in some ways perhaps it does—the children belong to the master even if the wife does not.
But Rava does not read it that way. He reads it as referring back to R. Yose the Galilean. The children belong to the mater only if the mother does as well. If the mother does not, then her children born to her when free are also free. Yeah!