Missing

You give way to little details about the party and the end of the short story doesn't really make since to me. You should talk more about the mom in the story, you just bring it up out of no where and it was just to brief. It's still a good start but i think you still got a ways to go.

Sorry!

It's a good start, and it left me asking a lot of questions, maybe too much. It didn't really answer enough questions to let the reader know what they're actually reading. And I know it's hard sometimes to give the needed information without making it too obvious. If you cover the rest of the stuff early on then it should probably work out fine. Hear's some question suggestions.

1. What genre is the book?

2. Who else was at the party?

3. Why would her dad agree only to explain her mom's disappearance on her birthday?

4. What's the approximate time frame and setting?

I hope to hear more.

words&wishes

You give way to little detail about anything If this was the begging of a book or serious it would be good because it gives curiosity and we wonder what this is, what happened, did the dad do something?

These questions are good hooks that are excellent for the begging of a book, but just as a short story it’s just plan confusing and irritating for the reader. You show promise in this so I suggest making this longer and to answer these questions in it.

It is a good start. I like the idea, but you need to give more information. We don't know about her, or her mum. How long gas she been gone? Where? Why? it is still more of a prologue than a short story. if we don't know anything, we don't consider it a story, just some text.
You have also some grammar mistakes:(My opinions will be in a parenthesis)
I blew(,) and the orange flame disappeared leaving a perfectly square lilac coloured cake.
I picked up the knife, judged the angle(, and) then pushed.
It was so rich I could hardly manage it(,) but I persevered, a grin plastered on my face. 
“Well bye then(,) everyone,”
"(S)ee you tomorrow!"
I fled to my room, tears cascading down my face, cursing my foolishness(,) but also thanking myself that I had stopped there and didn’t hear the rest of the tale. 

I Wish we could know her name, her age, a little more about her. (It is a her, right?)
I enjoyed it, but it could use a little work.
~Lili

Hey there, firepen!

This is pretty short, even for a short story. It's not really clear what the main plot of this story is. I'm guessing it's that the MC is wondering where her mum is, and I'm assuming she's missing, seeing as that's the title. But there's not really enough information here to give the reader a background to the story.

See, we don't know how long her mum's been gone. Referring to the last line, I'm guessing that her mum may have disappeared somewhere around the main character's birthday, as she says 'There was always next year.' It makes me think that she only brings up her mum's disappearance around the time of her birthday.

The narrator comes across as nervous when she thinks about asking her dad where her mum is, when she says that her eyes are watering in anticipation and when she says she can't eat the cake, I'm also guessing it's because she's nervous. The conversation is quick and rushed, leaving the reader reading it again to make sure they haven't missed anything. The dad's really dismissive about her question and she cuts herself off and runs away. If I wanted to know the answer to something as serious as where my mum was, I think I'd be a little more forward and determined to find out the truth. The shy and careful way she comes across may just be the character's traits but, seeing as I don't know anything about her, I'm just guessing.

There are so many questions in my head after I've read this that I'm left guessing a lot, trying to fill in the blanks myself. This story comes across as the bare skeleton and all you need to do to make it a more enjoyable read it to flesh it out. I feel that you do have the potential to make this great, but the lack of detail and background is holding me back from being able to feel satisfied after reading.

To be honest, I first thought this was going to be about a girl who wants to lose weight and I was waiting for her to throw up her cake after everyone had gone. You know, because she was so willing to make everyone leave. Then I thought it might be about a girl getting abused because she seemed scared to be alone with her dad. It's always great to let your reader try and figure things out for themselves. I always like to try and guess ahead of the story, but here you've left the options too open. It's almost like the reader's left with no option but to decide what the story was about for themselves.

My advice would be to add in some simple facts - When the mum went missing. How it's affected the narrator; is she losing weight? Quieter? Why she's so scared to bring up her mum around her dad. Just adding in these simple answers will help to cement the direction in which you want to take the story. Also, it would be nice to know the age of the narrator. You could always add that in when they sing at the start. Like, 'Happy 13th birthday'. A name would be nice too. A name is a basic human attribute, so giving your character one will help to make them seem more realistic and will enable the reader to build up an image of them in their head.

This may seem really harsh, and I'm very sorry if it comes across that way, but from the way you write I know you have potential to be great one day. It's just a case of making sure you give the reader enough background to a story so that they can read with the confidence that they know what's going on.

I hope this helps and if you have any questions at all, feel free to send me a PM or write on my wall. I'll be happy to help you some more

xDudettex