If you have a regular Vampire, I would have the Vampire Spawn work as a distraction from what the Vampire is doing. If the Vampire’s goal is to kidnap or kill a certain person. I would have the Vampire Spawn killing or dragging off regular weak townsfolk on the other side of town. A Vampire may not care much about their spawn past using them as a distraction or bait, while they do the important work. Such a Vampire Spawn would attack and kill townsfolk, livestock, or anything else it may desire to. You could even have the Vampire Spawn think it was growing more powerful by having non killed victims go along with what it is attempting to do. Having townsfolk defending a monster that is feeding on them presents all new challenges for adventures.