Rob and Kristen are still very young and have a lot of time to think about whether or not they want to start a family; but it sounds like Rob is very serious about staying with Kristen.
He had this to say to Vanity Fair on the subject:
“Not right now, but yes, of course”, “Not yet. We haven’t planned anything.”
Although he's not ready to become a dad right away, it seems like when he finally is ready, he wants to start a family with Kristen.
Do you think the two will eventually get married? Have kids?
source: hollywood life