This episode occurs in Chapter 23, and it is clear from the text that hearing Jim talk about his family has a massive impact on Huck, as it helps him to take another step towards seeing Jim as less of a slave and more of a human being who is exactly like Huck, even though he has a different skin colour. Note, for example, what Huck says about Jim in the following quote:
...and I do believe he cared just as much for his people as white folks does for their'n. It don't seem natural, but I reckon it's so.
This may seem incredibly bizarre to the modern day reader, but it must be remembered that at the time in which this novel was set, the selling of slaves and the separation of mothers and their children and even of husbands and their wives was "justified" by arguing that slaves did not experience love and family bonds in the same way that whites did, and therefore it was alright. Huck makes another very crucial step towards challenging the overwhelming racial stereotypes of his day at this point in the novel, which will culminate in his final decision to risk going to hell rather than let Jim return to captivity.