There is an Irish name ciara pronounced keer-ah, and an Italian name Chiara pronounced kee-ah-ra. I think that must be where a lot of the confusion comes in. The 'k' spellings are anglicisations, but it's unclear which version they are anglicising.
The route name for Kieran though is definitely he Irish Ciaran, which is traditionally pronounced Keer-awn, and on that basis I would be inclined to go I before e. But the 'e' throws it for me so much I think what I'd actually do is just google and see which variant is most commonly used of your two options in the uk, as the most annoying thing for the child will be correcting it.