Hi Meagan,
sorry I've taken so long to respond, this is a very, very busy time of year for me with work and publishing deadlines, but now you have my full attention! When a three year old hits and hurts others that much it is very different than a younger, preverbal child who hits because he is frustrated. By three a child should not be exhibiting this type of behavior so frequently. A few thoughts come to mind in thinking about this issue. First, I wonder if he has any expressive language difficulties. It is common for children to hit when they are upset or frustated and don't have the vebal skills to express themselves. It is also much more common for boys to have language delays than girls. My other thought is that living with a single father may be causing some stress in the family in general. For example, what is the child care situation like when he is working, do the children have issues w/ not having a mother around (is she in the picture at all?) How does dad do as a single dad? Are there other emotional issues in the family in general, unrelated to single parenting, that could be contributing to his behavior.
Keep in mind that a three year old who hits this much is telling you something and you need to figure out what it is. I wonder if it would be useful for dad to speak to a therapist/counselor to see if he can get some help. Hope this helps.