I'd call CPS. It doesn't sound like this is the type of person you can have a conversation with. What could you even say? Excuse me ma'am, I couldn't help overhearing you yelling at and smacking your kids the other night...? I'm sure that conversation would end well. /sarcasm.
Personally, I'd make the call. You know the kids are being hit, yelled at, belittled. That is child abuse.
Personally, I'd make the call. You know the kids are being hit, yelled at, belittled. That is child abuse.