In the real world, then probably even more than now, it isn’t necessary for the baron to rape young women. They throw themselves at him, as a rule.
A young woman who managed to produce a child for the lord could have the child recognized and be raised as a member of the aristocracy, albeit an illegitimate one. Though this usually applied when the woman was a member of the nobility or squirearchy herself. Serfs were pretty much below being noticed.
Although it should be noted that William the Conqueror was a bastard, the son of a tanner’s daughter. That’s pretty impressive social mobility for a single generation.
Same deal with slavery a couple hundred years ago. Given a choice between working the fields, or working the master's bed, a more-than-sufficient number of cute women would have voluntarily picked the bed.
At worst, the kid would have been given a tryout to be trained in arms, to be one of the lord's guards.