Okay so this is where I stop reading but it's for personal taste reasons (nothing to do with the slash, but I don't like it when children and adults match up as soulmates - personal preference though, I'm not criticising that development).
I just wanted to give a piece of advice with regards to storytelling that perhaps might help the readers feel more connected to the characters/story (I've read some reviews and several people complain that Harry & Sirius are just two OCs, or that the story is boring).
In my opinion, you skip some scenes that are very important to keep the reader connected to the characters & story. Time skips are great tools to skip boring bits (for example the journey from Bree to Rivendell), but the issue is that you skip interesting bits. You skip the part where Sirius & Harry tell Gildor & Arador about where they're from and who they're related to, meaning we never see their reactions to that knowledge. That would've been very interesting! It also would've relayed important information to the reader with regards to how believable their story is to inhabitants of that universe and how important it for these people is who Harry & Sirius are descending from, foreshadowing how they'd be received by greater (elven) society.
It's not that bad since Gildor & Arador are relatively minor characters (I think? As I said I'm stopping at this chapter), but then you do that exact same thing again with Elrond, who is a much more important figure to Sirius & Harry, since they're literally related and they descend from his lost uncles. Here it would've been vital to see his reaction past the initial shock, to see how he receives them, how he talks to them, how do his children and people react. You want the reader to be emotionally invested in the characters, but then you skip the most emotionally laden scenes, severing any connection.
Another important bit here that you skip is the integration of Harry & Sirius into elven society. We see absolutely none of that, and it would've been very, very interesting. (In general we see little to nothing of their reactions & thoughts to this world they're in, or how they feel about being here and being children, about not being able to go back, about them being effectively immortal elves now.)
As for Harry & Sirius just being OCs: you do kind of lose sight of their original characterisations and connection. Sirius is far too okay from the start giving Harry up to two strangers - trusting them because of instincts or no (personally I do think they trust far too quickly, but that would've been a minor hiccup), he has a parental type connection to Harry that would've become much stronger here, where Harry suddenly is almost a toddler and utterly dependent on him. Further, as the only person they each have (who is familiar, who is from their world, who they have an emotional connection to, with whom they share being strangers in a strange land with), they should cling to each other much, much more than they are. And in this chapter, where Harry is just whisked away Sirius waits obediently at the door until he falls asleep, which just strikes as utterly OOC to me. I mean trusting everyone or not, I feel he still would've opened the door or tried to look in through a window or something. He definitely wouldn't have been happy to have zero information as to what's going on with Harry.
I think when you transplant characters from one world into another, the more you take away from them of their original world, the more you need to ensure that there are still some things familiar to the reader. Taking away their magic and names wouldn't have been so off-putting to some people (I personally didn't mind, though with the background of OOCness it definitely lessened my emotional investment) if there had been something else familiar that stayed - for example Harry & Sirius' connection, or key aspects of their personalities (like Harry's independence, or Sirius' disregard of authority).
Okay, that's all I wanted to say. I hope I don't come across wrong; I just wanted to give some constructive criticism with regards to story craft. I do really like the premise, and I like that Sirius & Harry are more childish, seeing as they're literally children. I also quite enjoy domestic type stories where "nothing much" (a description I've seen in reviews but disagree with, but I don't know how else to put it) happens, by which I mean stories that focus on characters and relationships rather than some grand "let's take the Ring to Mordor" type plot. By the time this chapter came around I just wasn't very emotionally invested anymore.

Elrond as the Goblin King?
I love it!

baby names dot com is also useful since you can search all sorts of languages by meaning...

Thank you for a very enjoyable chapter.

Really enjoyed this :)

This was a great story. I really enjoyed reading it. Thank you for all of the timelines and really putting in the extra research in for this story, it really makes this story great. I also really appreciate that you didn't follow the fellowship and had Harry be apart of it. It was refreshing to read a story about what else is going on in the world without having to read the same scenes over and over again. I also really appreciate that you didn't make this story smutty, I mean, I enjoyed the hints of Harry's and Glorfindel's relationship, but it wasn't just long sex scenes everywhere. And that end bit with Arwen! I teared up a bit. I do, however, understand what that other reviewer was saying about how there really isn't anything that magical about Harry and Sirius. It is just them in Arda, no crazy spells. But I don't really mind that all that much. I guess it just felt like it might play in more, especially after the first chapter with Lucius and Remus talking about the bloodlines. It just felt like at any moment, a wizard was going to come busting in and mess stuff up. Also, I really liked the time jumps, it helped progress the story alot. Anyway, thank you for writing this story, I really enjoyed myself.

My biggest issue with this story was that it was on no way a Harry Potter story. No magic, different race, different sexuality, acting like a baby instead of how he normally acts, different name. Where is Harry Potter in any of that? I feel it was barely a lord of the rings story as it barely covered any of that story at all and just took place in that universe.
This story was also pretty boring. Some people go to a new world and grow up from children. That’s the whole story. Since the main story of Lotr is only tangently mentioned, there is no plot really.

Eh, it's all good. You were only a year off with him dying at 36.

Thank you, this is very well written

A really great Sirius and Harry as elflings story! Thank you for sharing this and good luck with whatever you write next!

I don't know if you are still checking the reviews, but just a small advice. You said that the year is 2891 of the Third Age, and that Arador is the Chieftain of the Dunedain. While at that year Arador was indeed around, he didn't become Chieftain until 2912 when his father died, so the leader of the Dunedain would be Argonui, not his son.

...holy crap that was long and boring.

I like this story. More chapters please?

nice. thank you for the story

I just started crying in the middle of algebra because of this chapter. Thanks