I remember a long time ago, I read this children's book. It was from a girl's point of view, and she had a little brother. There was this filthy family, of about five kids. They were horrible. They had "tamed" a bobcat and they kept all sorts of weird stuff. They sometimes went to school, and the teachers would always pass them, even though they shouldn't have, because they didn't want to have two kids of this family in the same class.
I remember that there was a Christmas play, and these kids took over all of the lead roles, by force. They just said "Hey, I'm going to Mary and this one here is Joseph. Okay?" The play director didn't want to displease these rascals, so he/she just let them, to the disappointment of the other kids. Of course, the play was a disaster and some lesson was learned.
Does anyone have any idea what book I might be thinking about?