same age, I've had DD have her nose rubbed in it by the little minx who had always had a problem with her, & turned out deliberately hadn't invited her to her up coming party, that ALL the rest of the class WAS invited too....DD didn't notice at first, neither did , so the little s@d then made a point of suddenly befriending DD, by playing hurt & upset & DD is a sucker for a sob story, so took to looking after her.........
little minx even announced loudly to me at home time, that she was so sorry that she hadn't invited DD, I thought it was a past party, & said "oh don't worry, I'm sure they'll be other parties".....until another Mum suddenly looked quite cross & piped up, don't worry, she'll be coming to my DCs house instead that day.....she then told me quietly that the party was the up coming weekend
....DD handled it EXTREMELY well, & I was very proud of her for that, she even made a point of inviting the same Girl to her own full class party, as she "wasn't playing those silly mean games"
So yes, can be a complete mind field from both sides, & some Kids can be little oiks & use it, but in the greater scheme of things, it is ALL good learning experience for our Kids, & helps them grow into well adjusted adults who know life isn't always fair, but can deal with that :).....even if we do sometimes feel like screaming at the time 