my friend told me this story a few years ago and i remembered it now while reading some of the other topics. anyway, he's got this very good female friend, whom all kinds of wierd stuff happens. and she told him that one time she was at her friend's apartment for a sleepover and it was kinda late. they were in her friend's room and they were having fun, when her friend said that she needed to go to the store (i don't remember what for), and told her to just keep having fun till she's back. so, she sits there on the couch and looks at some magazines. the TV was in front of her and it was off, and the door was behind the couch, and it was partly made of that milky glass (i don't know how you really call it, but you know what i mean). the door lead to a long hallway. so, she was flipping the pages, and she raised her head and looked at the tv. and since it was off, she could see a reflection of what was behind her. and she saw two white silhouettes of children (judging on the size), and they were just coming in little jumps (like kids sometimes do) down the hallway towards the door. she couldn't move at first, just stared at the screen and when they were almost at the door she made herself turn around and look. and there was nothing. just the door. her friend got back couple of minutes later and saw her all crying and scared. she told her what had happened and after a while her friend just sorta convinced her that it was probably nothing, that she was sleepy and stuff. but after a while, her friend went to the kitchen and came back looking scared and asked her if she opened that little window up in the store room. she said that she didn't, and her friend told her that they never opened that window cause you couldn't even get to it from all the stuff and that it probably wouldn't open after all the years. but it was now open.
i know it sounds like a common urban legend story and i don't even know wether to believe it. i mean, i believe the friend who told me but i don't know that girl from the story although she's a good friend of his. don't know, it still gives me creeps.

That is one creepy story. Any story with little kids creeps me out.

Sounds like a ghost, perhaps?
Spirits opening doors and appearing and disappearing, they are known to do that stuff.
Don't know whether it's real or not, but sounds like a brief incounter with a passing by spirit
I don't think these kids meant harm, maybe just having a little fun for themselves
If a spirit wanted harm, it maybe would knock something over?
Throw something at her?

But then again she might have just been pulling your friend's leg But who knows?