I did a quick search of our Old English noun category and I seem to have found at least one parallel for the e>i change in an a-stem: knehtaz > cniht, although this also has variants (cneht, cneoht); this seems to show the possibility, at least. I would still be very curious to see any theories as to the absence of *cind (< *kindą) in Old English and its connection to cild. – Krun (talk) 00:03, 23 September 2012 (UTC)
I think many people have wondered that, it is certainly curious. It's quite possible that the two words were mixed up in the early languages, and that cild took its z-stem inflection from *cind. But that doesn't explain the i, really. For eht > iht it's a regular change, but there is no parallel for elþ > ild. The closest we can get is gieldan from Template:termx, but that's -ie-, not -i-.