I would be really grateful for any advice or thoughts...Since Christmas I have noticed that my niece has been difficult when playing with my dd. My DD is a toddler she will only be two next month my niece is two years older and is four. This behavior began with the snatching away of toys and then hiding them and then refusing to let my dd play with them. I didnt like this behaviour but thought well this is what children do. However this devloped changed when my niece started taunting my dd with the toys that she would snatch away and hide. After this my DH and i decided that we would have to really keep a close eye on things when they were playing together.However at a recent family party she ended up having a major tantrum and screamed at my dd for no reason, later on in the day all the girls were upstairs my dh took dd up to the room as dd was walking into the room my niece started to slam the door into dd and she got squashed. It was deliberate as my niece didnt realize that my dh was behind and saw everything. He scolded her. Then later on in the afternoon she told my dd that she didnt want to be her friend anymore. Luckily my dd is oblious to most of these behaviours as she is too young to understand.I feel that the bullying is getting worse my siter thinks that this is normal for children to behave with each other like this. My DH and I came home after this party really upset. I dont have a clue how to approach this with my sister but I am going to have to cause if I dont then we will stop visiting them to protect our DD. Are we overeacting is this normal?