HELP! Found my daughter showing her knickers to the neighbours boys!

So I had popped to the shops yesterday leaving my eldest daughter 11 (still in uk primary school) playing with a few friends from the street in our garden.I came back ealry after forgetting my purse to an empty garden. I didn't think anything of this until I went into the house.I found my little girl standing in the middle of the room on my cofee table. She had her skirt lifted up exposing her from the belly button below showing the three boys and one other girl who were sat around staring up at her, her undies! I got the shock of my life seeimg my little girl stood in her knickers (bright pink disney princess no less!) In front of boys!I didnt handle it well as they was a bit of shouting as i sent the others packing at my girl to her room. Ive always brought my children up to be modest and this had really shaken me.Later when i spoke to her through her tearful embarrassment she told me she had lost a forfeit after a game they had been playing.I was dunfounded, my little girl had always seemed just that I couldnt belive she would play such a game!Is this normal? Did i over react? Has somthing similar happend to you?Please help I dont know how to approach this with her when I get home! via /r/Parenting http://ift.tt/28PwivR