Hmm. Hadn't really thought about that possibility (the child being Chaos), but I don't think it fits since Shinryuu is doubtlessly the dragon mentioned in the Chaos Reports, and it's also Chaos' summon.
Cid's got to be the narrator of the reports since he mentions losing his wife -- and since he apparently was the one to make a deal with Shinryuu, I'd think he'd be Chaos as well.
As for Garland, I admit that I'd always thought prior to Dissidia -- and even early on before we knew what these reports say -- that he was just a strong but otherwise normal knight possessed by Chaos' spirit or something.
But given his behavior in this game, his knowledge of the cycle, and the fact that he comes back after each death, I can't help but feel like this space-time distorting child was him -- especially since it was a powerful emotion that led to the space-time distortion happening in the first place. The Chaos Reports mention that Garland needs such a strong emotion in order to revive each time.
Also, the Cosmos Report (no. 7) where the distortion occurred mentioned that -- when the narrator was shot -- the child screamed and hate was reflected in his eyes as the distortion opened in front of him. Then, in the first Chaos Report, the knight was said to be "chained to the prison of time by his hatred born of love."
It sounds like Garland is the child to me.