What is Jinta and Ururu's Identity? Jinta and Ururu are the kids that works in Urahara's shop. I'm curious as to what their identities are. As far as I remember it was never been said what their background stories are.

Are they Shinigami like Urahara was? If they were, why are they with Urahara? Were they also on the run from Soul Society?

Or are they humans with special powers like Chad and Orihime? If they are, were their powers awakened from being close to Urahara, much like Chad and Orihime's powers being awakened by being near Kurosaki Ichigo.

Or are they Quincies? Although I doubt this very much since they never been seen using bows and Quincy techniques. Or are they modified souls like Kon?

What are they?
I would like to start off by saying that their race hasn't been explicitly stated in either of the Anime/Manga, so we can only theorize what race they might be from. Most of the evidence points to them being either Enhanced Artificial Souls/Humans.

Here are the possible theories, the facts supporting them and the facts opposing them:



Theory 1: They are Enhanced Artificial Souls1

We know that Nemu Kurotsuchi is the artificially created "daughter" of Mayuri Kurotsuchi. He used a combination of Gigai and Gikon technologies to bring her into existence. It's likely that Urahara did the same to create Ururu and Jinta.

For: 


They seemingly come from nowhere and live at Urahara's.
Both have powers way above anything else a human has shown in Bleach and Ururu even has an "angry-mode" when she gets hurt.
It shouldn't be hard for Urahara to create Mod Souls, regarding the knowledge he has about Souls, modified Souls and how they work. Someone who can create a Hogyoku can create Mod Souls for sure. Especially since Urahara didn't need to create them from scratch, as they already existed.
For Urahara to create a special Gigai shouldn't be much of a problem either.
He is the person who created the special Gigai that held Rukia during her two months in the human world.


Against:


It's not impossible for them to be humans inspite of their strength because Inoue and Kannoji are both humans but possess abilities greater than those of normal humans.
Unlike Nemu, they have a will of their own.


One may argue that they aren't robotic (they don't say yes to everything that Urahara says), but as Ayase points out in the comments, Kon is a Mod Soul but isn't robotic either. 



Theory 2: They are humans2,3

They are said to be High-Spec Humans on the Bleach Wiki:


  A very small percentage of the Human population develops a high amount of Reiryoku; they are known as "High-Spec" Humans. These Humans can see and interact with Reishi-made objects, such as Souls, to varying degrees and for various reasons.


For:


Urahara had the Hougyoku in his possession up until Rukia came to Karakura town and lost her powers. He lent her his special Gigai, with the Hougyoku hidden in it. They could have gained their powers from being somewhat near it. Sado and Orihime gained theirs as an indirect consequence of coming in contact with the Hogyoku, as it caused Rukia to lose most of her powers to IchigoSource, which as Urahara said, was the cause of awakening of powers in Rukia and Sado. From the Wikia article on Sado:


  Urahara then tells them that Ichigo's large amount of Reiatsu leaked onto them and that caused them to gain their powers, and that these powers are what they naturally had to begin with.

They age like normal humans, whereas Mod Souls do not age.


Against:


Given Urahara's expertise in the matter of Gigai and Mod Souls, it's possible for him to come up with a way such that Mod Souls age.
Even though they are stated to be High-Spec Humans on the Bleach Wiki, there is no official source regarding the same.




Theory 3: They are Soul Reapers

For:


They always hang around with Urahara and are knowledgable about the Soul Society, Hollows, Quincies and pretty much everything a standard Soul Reaper knows, although they might have just learned about it all from Urahara.


Against:


They do not have a Zanpakuto.
They do not have any reason to live with Urahara outside the Soul Society because they aren't exiled from the Soul Society, which Urahara is.




They aren't Hollows/Quincies

I say this because:


Their physical appearance does not match with that of a Hollow, such as having a broken mask or a hollow-hole. As the Wikia article on Hollow states:


  All Hollows wear masks, which are formed from the hearts they had lost as Humans. This mask protects the naked instinct which is left in a being after the loss of its heart, and obscures the original identity of the Hollow

Their appearance does not match with that of a Quincy either:


  The final point of contrast between the Quincy and Shinigami is their respective choice of uniform. While the Shinigami wear traditional, black, flowing hakama, the Quincy wear white, form-fitting, high-collared tunics. They always wear casual clothes. 


Neither do they seem to have the power to manipulate Reishi into spiritual weapons.