I read part of a book about a boy who could speak a language if he heard just a few words. He and his mother play a game where they slide on the floor in socks while she plays the radio and he learns new languages. However, his mom is later kidnapped and he goes undercover in illegal trade as a translator. It was a YA book that was part of a series about talented kids. I think one of the other books had a kid who was a talented thief and left a ribbon behind whenever they successfully took something. Anyone know it?