It's been too long since I've seen it - does it regress them to twelve years old, or recreate their twelve-year-old bodies? Logically it would have to be the first one, since their memories are all intact, but that doesn't mean it was, because the "personalities jumping between bodies" trope typically ignores the relevance of brain structure to personality. If it just recreated their twelve-year-old bodies, Picard would still have had a normal heart.