Hi! Interesting discovery! I remember watching "Power Play" and I remember how that young boy voice sounded. I didn't know that was an actual British accent. That's cool!
And yeah, I'm not sure whether or not Kayzie did that boy's voice.
By the way, it is indeed possible that they hired a kid to play the role. In the beginning of Pokemon, they actually hired a kid to voice Ash. XD And then, after re-doing the first episode (they recorded the first episode a lot of times, lol), they fired the kid, and then hired Veronica Taylor.