I'd agree with most, and simply give them the stats of the race they were brought up in, unless it's something specifically passed through nature, rather than nurture. For example, a Pictish babe, brought to Aquilonia would have the Aquilonian abilities, but may still be petrified of snakes.
The only problem I can see from this approach would be the changes in abilities, races have. Would a Zingarian raised in Hyperboria have the inheritad -2 to Constitution of his race, or due to the style of life in his new home, gain the +2 most Hyperborians have?