Out of curiosity, how do you pronounce ‘Allegron’?

I’d drop the comma. And is there any particular reason you chose to use ‘one’ over ‘they’? If not, I’d use ‘they’ instead of ‘one’.

I’d change the comma to a semi-colon.

While it’s not wrong, I think you can drop ‘to make sure they grew’. I feel like that’s kind of implied by the first part of the sentence.

Since you’re stating ‘king and queen’ as a title rather than ‘King Leon’ and ‘Queen Michelle’, you don’t need to capitalize ‘king and queen’.
Also, if they have their own king and queen, I don’t think you need to refer to it as ‘away from the rest of society of Britain’. If it’s its own kingdom, then it really probably doesn’t have much to do with Britain anyway.

I’d say ‘a child’ rather than ‘their own’, as that makes it sound a bit like they should be taking care of someone else’s child.

I’d use “didn’t” instead of “never”. ‘Never’ is an absolute, so by using that with ‘much’, it doesn’t work well.

I’d put a comma after ‘ignorant’.

I understand what you’re trying to get across, but the sentence structure seems a little confusing. I suggest simplifying the sentence.
“The town was often denied to him. One night changed that.”

‘… the next time they were opened.’ You just forgot a word.

‘bangs’ instead of ‘bags’, yeah?

I’d change the comma to a semi-colon.

Since this is a different person talking, I’d drop it into a new paragraph.

‘led’ instead of ‘lead’.

I know this is a colorful metaphor, but it to create friction like that he’d have to be shuffling. So I got the image he was shuffling along the floor, which, unless he has some leg issues, kind of contradicts the image you were trying to get across.

I think you can drop ‘just’ and have the sentence flow better.

While I liked the description of the hallway, you didn’t spend any time telling how loud it usually was. (Save for the single line about the servants.) To really help the reader understand how odd the silence is, you have to tell us about how loud it usually is.

This isn’t an error, but I have a suggestion anyway. Since this is taking place in some form of Europe, I suggest using kilometres, metres and so on and so forth. Just for the immersion of it.

You might want to be more specific if you’re going to talk about it. Sure, he’d be reading things like The Prince (or whatever the cultural/political equivalent would be), but he’d also be reading all about economy, foreign policy, military strategies and histories, and so on and so forth.
Obviously you wouldn’t need to put all of this in (as it would just be really needless), but if you’re going to talk about it, being specific will make it sound more real. =]

I’d say, rather, that Alvar found this weird instead of having the author state it. It would give us more insight to Alvar as a character.

Why doesn’t he go back to the library? I mean, sure, it’s quiet, but at least the tutor was there. If he’s that frightened of being alone, why not check for Ms. Jacobson?

But he just came running out of the library, didn’t he? And if he’s panicked his legs would have certainly begun to circulate blood already. Any particular reason he didn’t?

I’d change the comma to a semi-colon.

‘now’. Just a little typo.

I think you could drop the comma.

I’d change the comma to a semi-colon.

I’d alter the sentence structure to something more along the lines of ‘… choking on it.’ You just stated that it was scent, so you don’t need to do it in the next sentence.

‘heard’

I think you can drop this sentence. If you don’t give us an answer, we can assume Alvar doesn’t know.

I don’t think you meant ‘smeared’. That makes me think his blond hair isn’t natural and the color is getting smudged out. Maybe covered? I’m not really sure what smoke would do to hair except make it smell awful.

Did you mean to have ellipses (three periods) or is there just one too many periods?

Since this appears to be third-person limited, I’d cut this sentence. How would Alvar know that?

Whose? Alvar’s or the man’s?

You might consider giving us a line where the man let’s go of Alvar’s neck. If the man didn’t, Alvar would have a sever tear in his throat when he fell down. I’m really hoping that didn’t happen to poor Alvar.

If his heart has stopped beating, what’s making him breath? If he’s going to be undead, I figure you should just have everything stop working. Unless this is a major plot point later on.

I’d put a comma after ‘himself’.

Now, maybe it’s just me, but if I had just gotten half-devoured and felt horrible, my first thoughts would be towards getting out of there instead of wondering what had become of me.
Maybe it’s just me?

I understand you’re going for repetition here, which I think is a good idea, but I’d change the word ‘needed’. By repeating ‘A need’ the feeling of urgency works well, but since ‘needed’ is so close to the word ‘need’ it just doesn’t… flow.

‘stake’ instead of ‘steak’.

I know you’re trying to get across his feeling without being vulgar about it, but this sounds a little… silly to me. Why not just, “… made him want to be sick”?

I’d change the comma to a semi-colon.

I felt like this happened really fast. I understand that the change happens quickly and that it changes a person physically and mentally, but this was so fast that I felt it missed a lot. A lot of the drama and suspense that comes from transformations in characters (both physically and mentally) is that we watch the character struggle with it. We feel for the character and the situation he’s in because the author takes the time to show the reader just how much this is affecting the character instead of just, “Oh he’s normal. And now he’s not. BAM.”

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I felt like this moved really fast for all the information and scene changes you put in. To really give the effect of time you’re trying to get across, I think you should elaborate on scenes. Maybe talk about what he’s actually studying? Maybe elaborate more on the labyrinthine halls? Maybe elaborate on the attack itself, both on the humans and then on the vampires-things?

You also mention how young the prince is multiple times. While I don’t think you need to give us an exact age, I think you should explore more of his thought processes and actions so that we have more of an idea of how young he is. I really couldn’t even wager a guess, right now. And if his age is important, which I got the feeling it was since you mentioned it more than once, I think you should explore it a bit more.
And if you decide to take my advice about elaborating scenes, you could kill two birds with one stone!

As it’s just the beginning it’s hard to form a good opinion. I think this could be a very interesting read; I just really can’t tell from the beginning. I think it depends on how you’re going to handle a lot of the upcoming plot points. You did have some interesting imagery inside the castle though, which was fun to read. And the way you described Alvar’s appearance, as well as the vampire-things was quite interesting. Overall you just really seem to have a handle on imagery!

Good luck with it!