My husband slapped me after I slapped him first. Our kids saw me slap him but not when he slapped me back

I'm still a little shaky, my husband and I got into an argument. It was stupid and in hindsight not that bad, he tried to leave the room to go and cool off so that we could re visit the conversation later and didn't want to deal with me and I followed him out of frustration, it felt so belittling at the moment, I admit that I over did it but he told me to get out ( we were in our room and his plan was to leave the room first) and I slapped him.

The second I did, I was so horrified and guilt ridden. My husband slapped me back and I was so startled I fell down, not due to the force. We found out that our kid saw my part and then quietly ran away to tell her siblings. I don’t know what to do, he left the house with the kids and they're at a shopping mall currently.

I know I was wrong, and I take full accountability for that. Please help!