My ds broken his collarbone from softly rolling off our bed (he's 2.5yrs and rolled on purpose) but as a leg I would highly doubt you could roll and break it! If so it is something that surely would require further investigation. I think the fact of the matter is a eg doesn't break when a baby rolls over, they are obviously lying. It is very sad that your sister is pushing the blame towards you when it is obvious your kids are lying I would be very intent on finding out the truth if I was her. Why are her kids lying etc etc

Perhaps your nephew is just badly behaved maybe it comnes from a lack of discipline or a form of disorder or learnign difficulty or perhaps something more serious as has been suggested. I guess the best you can do is nicley talk to your sister about your concerns and hope she does something about it.

I hope you dd heals really quickly, I am so sorry I know how horrible it feels to have a child with a broken arm. xo