I really like my husband's sister but she has an apparently unpredictable, aggressive 4.5 year old son who apparently bites. We're going to visit them this weekend and it's the first time we're meeting her son (we've only seen her with her older daughter). I'm really concerned about how he's going to be with my 5 year old boy who's lively but not aggressive at all. Any advice on how to stop/deal with a child who bites?