So a bit of background,me and my ex partner split some time ago,he has no contact(through his choice) with our two children, my ex sil lives on the same street as us and reports back everything we do to my ex so our relationship has become distant, the issue however is that she has a child who is similar age to my children, theres a small group of children on the street who all play together on each others gardens and apart from the usual kid fallings out get along fine. However, when this child (8) is out there is always issues he is aggressive,violent and shouts and swears at other children, including to the adults whose garden he is in, he breaks toys or games without remorse and he is often sent home as children are left in tears, which results in him mum coming out of the house and shouting at the children for picking on him singleing him out and being mean however she refuses to discipline her child for his behaviour or see that he is often the cause of the problem. The lastest incident the kids were playing on the grass he came and stomped on one of the childrens heads...her response was "well she shouldnt have her head so close to his foot". My issue is that as my children are cousins of this child, she is often nastier to my children and tells my children they are bad cousins for not wanting to play with him and need to play with him and no other children. My eldest child comes inside in tears on a regular basis due to what her aunt says to her about being a bad cousin, I know my children aren't angels but are disciplined when needed, there is always an excuse for his behaviour and no punishment and blame put on others.sorry for being long winded but my question is how do I deal with this without getting into a full argument with her?I don't want to fall out with her but I can't sit back and do nothing when she is constantly being mean to my children and other children but claiming her child is an angel