I tell DS, that hitting hurts, it hurts my hand/face/leg and it hurts my feelings, it makes me sad. We use gentle hands. And ask him to show me gentle hands.
If he continues I ask him to use gentle hands or I will walk away.

I'm not sure when he started but he was quite young. I work on, if I can get a sentence out in one breath, it's not too long. Lol and seems to be working so far.