EXCLUSIVE

"Sons of Guns" stars Stephanie Hayden and Kris Ford were arrested Friday in Louisiana ... for allegedly hitting a 9-year-old boy with a belt so hard he bruised.

Parish of Livingston officials tell us Kris abused Stephanie's son from another relationship last month ... by striking the kid on his lower buttocks area.

Stephanie was also taken into custody ... because her son told cops she was present in the room. She's not being accused of hitting her kid.

As we previously reported ... Stephanie's dad Will Hayden was taken into custody back in August for allegedly molesting his other daughter -- and since then, he's been charged with another rape.