I like both.
Maia is a little younger than
Kaia but also older (it's a kid or a maternal figure but not in between).
Maya is definitely younger (anywhere from a baby to a 30-something.)
Kaia seems like it could fit any age and it's a bit "cooler" (not cool like popular but like cool like blue as opposed to orange/red). Both names seem friendly, but
Maia moreso.
If I had to use one I don't know what I'd pick. Either
Maia or
Kaia (but not
Maya, even though I like that spelling too).
I've met a Kiah pronounced
Kaia, but it looks like it's pronounced
Kia.