Whom do you consider to be "good kids?" My husband and I use the term for our kids or other kids when they are polite, helpful, or do something kind.
At the shelter, "good kids" are judged pretty much the same way.
At home, before they arrive at the shelter, though, the kids are considered "good" by the abuser when they obey his commands without question, don't challenge his beliefs or behavior toward Mom, and do everything he asks as quickly and perfectly as possible.
Of course, the abuser expects the same behavior from his partner. Otherwise, she is ungrateful, bad, stupid, crazy. After a while, she doesn't know what she is.
To the mom in a violent home, her kids are "good" when they warn her of a problem or fix it themselves, let her sleep and take care of sibs and household tasks when she is depressed or injured, protect her from the abuser by lying or begging him to "stop fighting" or "leave her alone."
The abuser doesn't want the kids to ally themselves with Mom. It decreases his power. As they get older and are "good" to Mom in ways that interfere with his abuse, the kids become ungrateful, bad, stupid, crazy...And often abused.
How twisted is that?