I look after my niece and nephew everyday before and after school as their parents work long hours. Today is DNs 9th birthday. DN has just started in Reception and DN is year 4. My nephew has been great with not asking to help open presents (my niece always nags him to let her help him) and really kind in making her a card off his own back, asking to bake her a cake and picking her a gift from his own piggy bank.
My niece had a few gifts at my house this morning (from me and grandparents) that her parents had said it was okay for her to open before school. One of the presents was wrapped in Frozen wrapping paper. My niece detests Frozen and actually sneered when she saw the paper. My nephew LOVES Frozen. He asked if he could please have the wrapping paper so he could use it to make a picture. She snatched it up and screwed it into a ball then dropped it into the dogs water bowl 
My nephew sobbed and went into school crying for the first time since starting, saying he doesn't understand why his sister is so mean to him. I spoke to her and told her how unkind she was but she shrugged and was unrepentant. I was going to take her out for cake and bowling after school but I feel like cancelling now. DP thinks it was normal sibling behaviour but I think she was cruel and shouldn't be allowed to continue to be like that (she has form.) Her parents are unreachable unless it's an emergency and I have permission to punish as I see fit. WIBU to cancel tonight?