I think there are two components here, linked but not causally, if that makes sense.
I’m just going to get this bit out of the way, as I don’t like typing it, but I think it is true anyway………….I don’t know why you thought playing around with his face and cap was a good idea – why would you want to distract someone who was driving? You were deliberately trying to get a reaction out of him while he was driving you and your children. That’s a phenomenally daft thing to do, and potentially put everyone in the car at risk. That does not in any way shape or form possibly justify or validate his reactions – his actions are massively disproportionate and clearly constitute assault – but it was still daft. This is not victim blaming, but it is also not a zero sum situation: you can have done something wrong without deserving the insane retribution it brought from your husband. His actions, needless to say, also jeopardised everyone in the car.
We all get stressed, especially when there are kids to raise, but I can’t think of a time I would have entertained raising my fists to someone I truly cared about. Even in the heat of a bitter argument it has never been close to happening. What he did was some completely out of order I find it worrying that you are minimizing it. Quite beyond the immediate physical damage to you, it also represents an enormous lack of basic respect for you as his partner. If I saw my father hit my mother when I was a young child it would have had a catastrophic impact on me and my perceptions of that relationship.
As for where you go from here, that is entirely in your own hands. If you want to leave there will obviously be difficulties and obstacles – it won’t be easy. That said, will you ever be fully at ease, let alone happy, to spend the rest of your days with someone who when he gets stressed can lash out physically? Where is the line for you? When he does it again? When it is not you but your children in the firing line? I agree with the other posters in that he needs to remove himself from the family environment while he gets some help, assuming he is willing to entertain such a path. If he refuses, then I would contact the police and leave it with them. Protecting your children’s emotional / physical wellbeing must trump everything else. Personally, as difficult as it may be, If my wife punched me in that circumstances I would be seriously looking at going to the police.
I hope you find the space to heal and deal with this, but don't feel like you have to put up with it if you don't want to. You can find someone better for you and your children.