They will do everything in their power to protect the Dragonborn's children from bandits and other random attacks.
With Hearthfire installed, you can also gain housecarls from Falkreath, Hjaalmarch, and the Pale's Jarls after purchasing land (Winterhold alone does not have purchasable property). In order to earn a housecarl, you must become a Thane (in other words, an acknowledged hero of the hold), which generally involves directly assisting the Jarl in question, helping the citizenry of the hold, and, in the case of the major holds (Whiterun, Eastmarch, the Rift, the Reach, and Haafingar), purchasing property. Housecarls are warriors assigned by the Jarl of a hold to protect the Dragonborn and their property.
