Tubalcain:The problem is not those kids. It's your firiend. You've got to decide if her company is worth putting up with that. An assertive person would tell the friend "this is not acceptable" and end the visit. Until there's a commitment to change if it was me I wouldn't let those kids in my house or go to theirs while they're there.
Gosh, at last. I read through this thread and was thinking "what about the 'friend''? This lady is no friend if she allows her children to behave this way towards you. She may not mind that they have no manners around her - evidently she does not, as she allows them to act in this way - but she should not subject others to their bad behavior, particularly someone that she supposedly values.
It's a no brainer. If her kids are hitting you, they are no longer welcome in your home. If she's not willing to get them to shape up in order to keep your friendship, then she's not worth your friendship.
For all the law is fulfilled in one word, even in this; Thou shalt love thy neighbor as thyself (Gal 5:14)