Why are there pixies, etc. on the First but not the Source?

[Firlont]

I am here imagining the chaotic result of the twain ever meeting on screen. But yes, the bit about the children's souls was stated in ShB for sure.

[elioaiko]

The game is inspired by Ivalice universe. Tactics Advance 1/2 and FF12 technically take way in the past before Tactics.

In Tactics, there are some beasts, I don't remember which ones but none of the iconic races like Viera, Bangaa/Nu Mou, or even Moogles. Really because they didn't come up with the races until 12 and Tactics Advance which came over way after Tactics.

I believe it was explained that a cataclysm took out most, not all of the iconic races aside from humans which is why we don't see them in Tactics because they're either in hiding, extincted, or not longer on Ivalice.

So it's not far fetched to say that The Shards and The Source have a similar situation.